In an effort to shift the burden of proof, some modern atheists define atheism as a "lack of belief" in God, rather than the classical definition "the belief that there is no God". As a Theist, specifically a Christian, I don't really have a problem with this. Yes, it is certainly easier to just say "prove it" when atheists say "there is no God", but it doesn't take too much effort to show that Christianity is a reasonable faith.
When atheists choose the easier route and just say "prove it", one relatively simple argument that at the very least shows a god exists is the Design Argument. Design, of course, requires a designer. Even relatively simple designs, like a mud hut, don't just pop into existence.
Let's talk about that mud hut for a moment. Suppose you and a friend just happen to find one standing in the middle of a forest. You don't see a designer. Given the finite nature of man, maybe you will literally never see him. It is possible the designer died and decayed long before you showed up. Or maybe it was just a temporary shelter before the designer moved on. In either scenario, it's possible that the only available evidence you will have that someone designed the mud hut would be the mud hut itself.
Now, what would you think of your friend's mentality if, rather than just accept the obvious conclusion that the designer exists, he simply said "now, I'm not saying there is no designer, I'm just saying I lack belief in the designer until I see evidence"?
Some atheists think they have a good response to this. "Well, we've seen people build mud huts". Ok, so are you saying if you never saw someone build a mud hut, you'd be totally cool with the idea that they just made themselves? Human beings are ridiculously creative. We see unfamiliar man-made objects all the time. Sometimes, we're not even talking about functional objects. We recognise design in art forms! Archaeologists might even find stone objects, which they have never seen before, and assume a man, whom they never met, designed it, even if they have absolutely no clue what it does. If it even does anything. They don't often assume nature just did something weird with a rock, they know there was a designer involved. So really, by making this counter argument, atheists aren't making their rejection of the Design Argument more sane, they're admitting the power the argument has, exposing their bias, and really making themselves look as crazy as someone who believes a mud hut could come about without a designer.
As it happens, the reality in which we live, and even the very bodies with which we live in it, are all significantly more obviously designed than any mud hut. In fact, God is such a brilliant designer, we actually copy God's designs to refine our own. It's called "biomimetics". And our copies always end up being significantly inferior to God's, so I think it's probably safe to say He wins. Furthermore, atheists often unwittingly admit this. I used to play a game: Spot the slip up. Whenever an atheist would use a phrase that acknowledges design in nature, I'd collect the phrase. Richard Dawkins ultimately won that game, when he wrote The Blind Watchmaker, in which he says "Biology is the study of complicated things that give the appearance of having been designed for a purpose..." He may have attempted to show why this appearance is illusory, but ultimately, he admitted it is there (and, of course, failed to show this appearance is illusory).
But as I alluded to, there is a difference between proving a god exists and proving which god exists. After all, humanity has believed in numerous gods over the years. That's even assuming any of us really have the correct idea of God. Obviously, we can rule out finite gods, which would themselves require a designer. We can also rule out polytheistic gods, which are rarely united enough to run a consistent creation. We can rule out capricious or deceptive gods for the same reason, with the added fact that really, we would have to. If you have an omnipotent deceiver to deal with, what can you possibly believe? You could be a chicken in a battery farm, and God's just tricking you into thinking you're a human. You would have no way to prove otherwise, because every proof you bring could be just another divine deception.
This, in itself, is one reason to trust the infinite, monotheistic, consistent, Holy, honest God of the Bible. Two assumptions must be made in order for any discussion to be logical: 1. Truth exists, and 2. we're capable of finding it. If truth does not exist, there is no truth to find, and thus no point in discussing it. If truth exists, but we cannot find it, there is no point discussing it because there is no way we can come to an adequate conclusion. The problem is, these assumptions are, in and of themselves, a conclusion. How do we know truth exists? How do we know we are capable of finding it?
This gets even more complex when we consider that, even if truth exists, the ability to find it is not distributed equally. The first requirement to seeking truth would be consciousness. A rock can't seek truth. A tree can't think about reality. Try having a discussion with a fly trap, see if it will do anything other than absorb the carbon dioxide in your breath.
But even conscious beings do not have the same truth seeking abilities. Do you think a chicken can tell you why it crossed the road? Of course not, it can't even comprehend the jokes that are made at its expense. Some dogs are said to be as smart as a 3 year old. My dog is a bit derpy, so he probably isn't even that smart, but suppose we take the smartest dog on earth. Do you think you could teach it to speak English as well as a toddler? And as smart as toddlers are, put them against any adult, the adult will win most games of wits. Will the adult have the same luck against another adult? Maybe, maybe not. It turns out, there isn't even a smooth distribution of intelligence among adults!
Or is there? If it turns out there is no truth, or we're not capable of finding it, intelligence is evenly distributed, because it isn't distributed at all. Or perhaps, by sheer coincidence, some people are capable of discovering truth. How would we know we're one of them? Perhaps the only person capable of discovering truth has discovered something that makes the rest of us think he's crazy?
All of this ultimately forces us to resort to circular reasoning. We could say that we think we can think correctly because we correctly think we can. Personally, I wouldn't rely on such logic. A drunk man might think he can drive, he'll regret that decision when he's serving 15 years for vehicular manslaughter.
So what's the alternative? Well, if you have to resort to circular reasoning, at least figure out a good place to begin your circle. The Bible gives us a good idea: The fear of the Lord is the beginning of wisdom (Psalm 111:10; Proverbs 1:7; 9:10). On its own, this isn't that impressive. But when you factor in all of God's attributes, and the fact that, using the assumption that we can reason, we have plenty of other reasons to believe in God, suddenly it makes sense. An omniscient, omnipotent, honest God is both the source of truth, and designed us to be able to seek it. God leads to reason, reason leads to God, God leads back to reason, and reason leads back to God.
But of course, that in itself isn't enough. After all, what if someone does prefer to just assume the power of reason? Rather than turning this into a battle of whose circle is better, let's just grant that human beings, whether designed to reason by God or not, can reason. So, do we have any more reasons to believe in God? Specifically, the Christian God?
Let's go back to the mud hut analogy. Your friend has conceded your point. Ok, the mud hut was built by someone. But who? You rule out termites, knowing full well their mounds don't look like this hut. You rule out monkeys, they don't build these huts either. You rule out tigers, they don't even live in this region. So what's left? A man.
At first, this is just a possibility you entertain. That is until you enter the mud hut, where you find a journal. This journal documents the story of three men: A tour guide, and his two clients. There is brief mention of freak weather conditions that force them off course, though it's not specific. We're then told that the tour guide, knowing it would be impossible to return home before nightfall, constructed the mud hut as a temporary shelter. This portion of the journal is signed by one of the clients. On the next page, you see a similar account, this time signed by the other client.
Well now you have a pretty good idea of who built the mud hut. It was a tour guide, as was testified to by two independent witnesses. This hypothetical journal would be far weaker evidence than the Bible is for God. The Bible, first of all, contains more independent witness testimony. And I mean it literally contains it. It was not originally just one book. Rather, it is a collection of 66 historical documents (depending on how you divide the books). Of course, you have to affirm divine inspiration to accept that Genesis is eyewitness testimony, so that's not a good argument for someone who doesn't believe. But the four Gospels (Matthew, Mark, Luke and John) were written by Apostles (Matthew and John), by a historian who interviewed eyewitnesses (Luke), and possibly even dictated by Jesus' closest Apostle (Mark, which, if not outright dictated, seems to have been at least heavily influenced by Peter). All of this within the lifetime of those who knew Jesus. And if Jesus had been a normal person who lived to be just 80 years old (which, according to Psalm 90:10, would not have been an unreasonable life expectancy even in His region at the time), most of it would have been written during His actual life. And that's just the four Gospels. I haven't even begun to touch how much respect the Bible has as a historical document, even among non-Christian historians. Not that I'm appealing to authority. I'm merely trying to condense the gigantic amount of historical evidence into a length short enough for a Facebook post. You'll see why I've done this as you read on, because I certainly haven't finished yet.
The long and short of the Historical Argument is that the Bible is the one and only Holy Book to be strongly historically verified. Not perfectly, of course. Evidence tends to decay if given enough time, which 2-3,000 years certainly qualifies as. Not to mention battling cultures tend to give conflicting accounts. But when it comes to historicity, the Bible is without equal, even among other/non-religious sources from the same time. Interestingly, when there is overlap, the Bible is sometimes the first and best historical source. Sometimes, it is even the only source, until new evidence shows up and confirms it.
A popular example of the latter is the Hittites. For centuries, the Hittite culture just disappeared off the face of the Earth, leaving the Bible as the only source of knowledge of their existence. Sceptics argued (based on circular reasoning, which we'll get to in a moment) that because the Bible was the only source that mentioned the Hittites, therefore Moses (the first Biblical author to mention them in Genesis 15:20) must have made them up. That is until the early 1900s, when the Bible was vindicated by the discovery of the Hittite capital city, and other evidence that subsequently came to light. Today, we have a great wealth of information about the Hittites.
So, why did I say the "Hittites didn't exist" argument is circular reasoning? The simple answer is because it is. While it is certainly preferable to have multiple historical sources about a thing's historical existence, or an event's historical occurrence, this is not always available. It turns out, a lot of things we know about history are known from only one source. (Ironic side note: Some atheists like to use these in an attempt to show the Bible is in error). The fact is, in order to discount the Bible as a legitimate historical source, you have to first assume it is less legitimate than any other historical source. When asked "is there any evidence this Biblical event happened?", it is entirely legitimate to say "yes, the Bible records it". You cannot reasonably discount the Bible just because it is the Bible, for the same reason it wouldn't fly if I said "it's true because it's in the Bible".
What's especially powerful is that the Bible doesn't just accurately record history after it happens. That's impressive enough, but even humans can do that. Meanwhile, the Bible also records history before it happened. This is called "prophecy". Predicting the future is hard. It usually requires an active attempt to fulfill the prediction yourself (e.g. saying "I will jump", then jumping), or just making an educated guess (e.g. the clouds have gone dark, so it will probably rain soon). If predicting the future was easy, casinos would never succeed, wars would never happen, and horoscopes would become significantly more reliable. As it happens, even predicting that you will wake up tomorrow, much less what time, is often a shot in the dark.
How is it, then, that the Bible has a grand total of 0 failed prophecies? Sometimes, the Bible's prophecies are so accurate, sceptics will attempt to post-date the book they're contained in. The book of Daniel, for example, was written about 550 B.C., long before any of the prophecies found therein were fulfilled. Yet, modern sceptics try to date it to the 2nd century B.C. Why? For no other reason than that to do this enables us to say Daniel was written after the events it prophesies, rather than that he was actually writing prophecy. Does the original language support this theory? No, the original Daniel was written in the common language of the culture during the 6th century B.C. Does contemporary evidence support the later date of Daniel? No, there are some quite old documents that reference Daniel, and the first attempt to date Daniel later is by a pagan named Porphry, in the 3rd century A.D. (his reasoning also being the accuracy of Daniel's prophecies). Is there any compelling evidence at all that supports the later date? Just one: The accuracy of Daniel's prophecies.
You'll notice a lot of anti-Christian arguments require circular reasoning like this.
Atheist: There's no such thing as prophecy.
Christian: Here's one in Daniel.
A. That can't be a real prophecy.
C. What makes you say that?
A. Because there's no such thing as prophecy.
The irony here is that, once again, the atheist has conceded the strength of the argument by resisting it so much. If prophecy was not such strong evidence for God, atheists would have no problem just admitting that it exists. Because they go out of their way to deny the evidence right in front of them, they ultimately show that it is strong evidence, against which they are heavily biased.
All of this comes together in one man, who just happens to be the most significant figure in all of history. Not just in Christianity, but in general. I am of course talking about Jesus of Nazareth. Literally all of the above affirms Jesus. Jesus affirms the infallibility and inspiration of the Old Testament, up to and including the Genesis creation account. Jesus demonstrated power over the creation by doing miracles that, even with our vastly superior technology, and greatly increased knowledge (as compared to the technology and knowledge available to men in the first century), we simply cannot replicate. Jesus is testified to by multiple independent witnesses. These witnesses are not all Biblical writers, nor are they even all friendly. Several hostile sources testify to the existence of Jesus, even putting their own spin on it (e.g. "He did His miracles because Satan helped Him, not God"), rather than just denying He existed, which would have been far easier to do if it was remotely valid.
On top of that, Jesus fulfilled a significant number of Old Testament prophecies about Himself, which is statistically impossible for a non-divine human being, even with conscious effort. With all of this combined, Jesus demonstrated His power over creation by going to the cross, just as was prophesied, dying, just as prophesied, and rising again, just as was prophesied. No other so-called "god" can make such bold claims and get away with it. Jesus? It takes a lot of slinky arguments not to affirm these bold claims and get away with it. In fact, some sceptical historians, such as Bart Ehrman, advise their students not to even try to explain away the evidence for the resurrection, because Christians are just too good at dismantling such arguments.
So, what evidence is there for Christianity? Basic logic: Creation testifies to a Creator. The existence of reason: Either God exists, or we can't account for why we can know anything short of our own existence. History: The Bible testifies to itself, and other external evidence affirms it. Prophecy: God tells history before it happens, and it happens. Jesus: all of the above combined makes Jesus the ultimate, undefeated contender for the title of King of kings, and Lord of lords. And my friends, this article (which was originally just a Facebook post) is but a minor sample of the evidence for Christianity.
So the question now is, so what? We have a Creator, we know who He is, why does that matter? Well, the first thing to consider is that we are His creations. It's kind of important for a creation to do what it was designed to do. The second problem is we didn't. Or, more accurately, we don't. On a daily basis, we do things He explicitly commanded us not to do. Or don't do what He has commanded us to do. And even without hearing those commands, He designed us with instincts telling us when we're doing/not doing these things. And as the Design Argument shows, He's also left us with enough evidence to naturally infer He exists.
What typically happens when a creation fails? The most common solution is destruction. If good is an enemy to evil, a good God is an enemy to evil men. And so we suffer death. Twice, actually. The first is a separation from the mortal realm. The second is a separation from God in Hell.
But that's where the good news comes in, because God does not desire this outcome. He chose instead to send Jesus, His only Son, to be born of a virgin, live a life completely free of evil, and then, instead of punishing us for sin, Jesus died, suffering the full wrath of God on our behalf. But He didn't stay dead. He rose! We are now faced with a choice. Faith, which I believe this article has demonstrated is more than reasonable, results in our sentence being completely overturned. Rather than suffering the second death, we instead inherit eternal life. Alternatively, refusal of this gift results in the one thing God owes us: The full punishment for every last sin. Choose wisely.