What is Unconditional Election?
Unconditional Election states that God elects who will be saved not according to any characteristic or deed of the individual, but according to His divine will. By contrast, Arminianism teaches Conditional Election, i.e. God looks right into the future, sees who will choose Him, and then elects based on who will accept Him.
The Bible Brain Position
Other than Perseverance of the Saints, Unconditional Election seems to be the most defensible of Calvinism's doctrines, and also happens to be the one Calvinists are most capable of defending. They will religiously swear by Romans 8 and 9, often just name dropping those chapters as if they settle the debate. However, within Romans 8-9 is the dreaded Romans 8:29-30, which states "For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren. Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified."
That statement "for whom He foreknew" is by far the hardest element for Calvinists to deal with, and generally, at least in my experience, they don't even try. 9 times out of 10, you bring up this verse, they will simply assert that foreknowledge has nothing to do with it. Yet, it's right there in the verse, within the very chapter Calvinists swear by. But I do think Arminians tend to oversimplify it as well. I've seen Arminians flat out say that foreknowledge and predestination are indistinguishable. "Predestination is foreknowledge", to quote one Arminian I spoke to. But that isn't what the verse says either. It says whom He foreknew, He also predestined. The way I used to explain this issue is that "the future affects the past as much as the past affects the future". I have since amended it to God's foreknowledge of the future affects how He behaves in the present. God, as we all know, is timeless. He isn't progressing one day to the next, as we do. Rather, every point in human history, including those that have not yet happened from our perspective, are all within His view, and all within His control. This means He knows everything that will ever happen, because to Him it already has. But God isn't omniscient just because He's seen it. He's omniscient because He's God. That means He also knows everything that ever could happen, and is fully aware of how to make that happen.
This can be seen in the examples of Tyre, Sidon, and Sodom. God knew exactly what would happen if Jesus had been sent to Sodom, Tyre, or Sidon. According to His own words, if Jesus had gone to those cities and performed His miracles, these three cities would have repented, and not been destroyed. This also puts Unconditional Election into perspective, because what we see here is people who would have accepted Christ, yet God still did not elect them. We see, then, that God's foreknowledge does play an important role in election, yet election is not conditional merely upon the people. This is a point that Calvinists need to understand. Just because God's foreknowledge plays a part in predestination, as we are explicitly told in Romans 8:29-30, does not mean election is conditional upon the elected people. God maintains His sovereignty at all times. But He does not show partiality. Acts 10:34, Romans 2:11, Ephesians 6:9, and many other verses tell us this is so. There is no partiality with God. Thus, though election itself is unconditional, God isn't picking at random either. He knows what, if anything, would make a person come to Him, and then, according to His wisdom, He chooses whether or not to do those things.
Let us take Paul as the example, God knew what would make Paul convert. Paul, by his own confession, was ignorant (1 Timothy 1:13). Had God left him in this state of ignorance, Paul would have continued persecuting the Church until he eventually died and faced the Lord in judgement. But in His mercy, the Lord appeared to Paul, removing that ignorance. God foreknew Paul. He knew what Paul would be if he'd been born in China in 1950 instead of Israel in the first century. He knew what Paul would have been if He'd made him female instead of male. He knew what Paul would be if he'd been born into a different family. Every aspect of Paul's life, God planned out from beginning to end. We see, then, how Paul's potential futures affected how God worked in his actual life.
The same is true for us. God knew who you would be with the parameters He set for you. Every letter in your genetic code was written by Him. Every event in your life up until now, He set up according to His wisdom, like a master chess player. He knew you would accept Him, and He knew how to bring that about. But He also chose whether to do so. It would be 100% just for Him to just leave you in your unbelief to perish. This, for reasons I am quite content to leave to Him, He did with Sodom, Tyre, and Sidon, who though they could have repented, were never given the signs they needed to do so. With all of this information, I contend that Unconditional Election and Conditional Election are actually both wrong, as like Calvinism vs. Arminianism in general, they overemphasise that which ought not be emphasised, and undermine that which ought not be undermined. Salvation is from God, and God alone. He is completely sovereign, deciding whether or not He will offer it, how He will offer it, and how much of a push He will give us to accept it.
<- Total Depravity - Limited Atonement ->
Woe unto thee, Chorazin! woe unto thee, Bethsaida! for if the mighty works, which were done in you, had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes. - Matthew 11:21 KJV