Atheists often take issue with the question "why don't you believe in God?" They often claim that the onus is on the Christian to give evidence for God's existence, and that their only reason for not believing in God is that they've just never been given any. So, theoretically, evidence should be enough, right?
But then you dig a little deeper. You get into the discussion, you start providing evidence, and suddenly it turns out the atheist has given it a lot more thought than they claim. They don't just reject Christianity because they have no reason to accept it, there is always, with no exception that I've ever seen, a reason the atheist resists the evidence you provide. Let's bring in our old friends Bill and Ben to give an example.
Bill: Why don't you believe in God?
Ben: I've just never seen any evidence for God.
Bill: So if I give you evidence, you'll believe?
Ben: Sure.
Bill: Ok, so let's start with prophecy.
Ben: Well actually, Jesus predicted that His generation would not pass away before He came back...
Why couldn't Ben have just said that in the first place? (He's wrong, by the way). It's easier for Ben to just claim "there is no evidence" because that forces the Christian to do all of the work. Ben's own views aren't scrutinised, and Ben has a number of arguments he knows that he hopes Bill doesn't.
But it gets worse. Most of Ben's arguments don't matter to him. If Bill can show that Jesus actually didn't predict His return in the generation that heard Him speak, would he convert? Probably not. In fact, he might even reuse the argument when Bill isn't in the room. My experience with atheists has been that they even use the same bad arguments more than once against me. That's just ignoring the ones I've caught re-using arguments they admitted to me they knew don't work.
So what's really stopping Ben from believing? If Ben is dishonest enough to use the same refuted argument twice, the chances are it's really just his own heart. You cannot convince someone to believe something they don't want to believe. But let's say he's not. Let's imagine Ben knows a large number of "problems" with Christianity, but in reality, only one or two are actually stopping him from believing.
Let's flip it. As an apologist, I'm obviously familiar with a range of arguments. Some big, some small, some I just wouldn't use because they're worth about as much to me as a chocolate coin wrapper is to a bank. My personal policy is it's better to know a few arguments well than a million arguments to a small degree.
"What would convince you to leave Christianity?" is a very difficult question to answer. Christianity has a doctrine called the Perseverance of the Saints. That is, a true Christian literally cannot leave Christianity because the Holy Spirit keeps them from falling off the edge. Thus, as a true Christian, I don't technically think it's possible for me to leave the faith. However, if Christianity is false, and there is no Holy Spirit preserving my faith, that means my faith is entirely intellectual. It is held together by several arguments which, if refuted, would give me cause to leave the faith. There are also several arguments against other faiths which, if refuted, would allow me to join.
Long time followers of this ministry will be familiar with some of my favorite arguments. The argument from reason, for example, is pretty solid. If the Holy Spirit does not exist, refuting the argument from reason would severely weaken my faith. This is because the argument from reason A. cannot be attacked without being proven and B. points to Christianity as the true faith while simultaneously pointing away from most, if not all others. If you can show me that there is another religion that accounts for human reason, and especially if you can show that Christianity fails to do so in a way I did not see before, you could convert me.
The question every rational atheist ought to ask, then, really is why don't you believe in God? It's never just a lack of evidence. There is always something, like the above, that keeps them in atheism and out of Christianity. So atheists, what are those arguments? Don't use the inconsequential ones that aren't stopping you coming to Christ. Think of the arguments that make you think Christianity isn't worth believing, then whenever you debate, use those arguments. Once they get refuted, do the rational thing and convert. Let the little arguments get refuted later on in your walk with the Lord.