Well, maybe you don't. That's fair enough. Although in that case, I would ask: why don't you believe in God? And no, this isn't an attempt to shift the burden of proof to proving that God doesn't exist.
Well, I'm sure anyone with an opinion on the matter managed to come up with some sort of answer to those questions quickly enough. So here's another one: why, or why not, do you believe that Jesus is the Son of God? Again, I'm sure most people can provide a response one way or another.
So here's something to consider. Why did the early Christians believe that Jesus was the Son of God? As a matter of fact, that question is one of the most important to consider in regards to salvation, the veracity of the Bible, and even the existence of God.
You see, many people will answer those first two questions with something along the lines of "the Bible tells me so". It may vary, some may provide more details than others, and some may provide additional evidence. But ultimately, the main factor in the vast majority of people's beliefs will be the Bible. And that's certainly not a bad thing - because the Bible IS how we should know these things. The real question is: why should we believe the Bible?
That's where a lot of people, both Christian or not, trip up. Atheists, especially, like to say that Christians believe that the Bible is infallible because God said so, and they know that's true because the Bible said so, and so on. This is, of course, circular reasoning. However, it's also a straw man, because a good case can be made for the reliability of the Bible based on objective reasoning and historical evidence.
So, let's get back to that third question. Why did the early Christians believe that Jesus was the Son of God? Paul actually directly states this in 1 Corinthians 15, and in no uncertain terms:
"Now if Christ is preached that He has been raised from the dead, how do some among you say that there is no resurrection of the dead? But if there is no resurrection of the dead, then Christ is not risen. And if Christ is not risen, then our preaching is empty and your faith is also empty. Yes, and we are found false witnesses of God, because we have testified of God that He raised up Christ, whom He did not raise up—if in fact the dead do not rise. For if the dead do not rise, then Christ is not risen. And if Christ is not risen, your faith is futile; you are still in your sins! Then also those who have fallen asleep in Christ have perished. If in this life only we have hope in Christ, we are of all men the most pitiable."
Paul makes it abundantly clear that his faith, and the faith of the entire early church, rested entirely and completely on the resurrection of Jesus from the dead. He even goes so far as to say that if it is not true, then Christians are "of all men the most pitiable". So what relevance does the critical importance of their belief in the resurrection have for us?
It tells us that the early Christians believed so strongly in that resurrection that they were willing to die for it. To be tortured, crucified, and killed. And this wasn't based on "blind faith". Paul made sure to give the church a reason for the resurrection, earlier in the chapter:
"For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, and that He was buried, and that He rose again the third day according to the Scriptures, and that He was seen by Cephas, then by the twelve. After that He was seen by over five hundred brethren at once, of whom the greater part remain to the present, but some have fallen asleep. After that He was seen by James, then by all the apostles. Then last of all He was seen by me also, as by one born out of due time."
Paul was not simply asking the Christians to believe in the resurrection so that they could have hope in Christ. He gave them a reason for that hope. He referenced direct eyewitness testimonies of Jesus being raised from the dead.
The fact that the early church accepted these testimonies is as critical to us today as the testimonies themselves were to their own faith. It tells us that the testimonies were reliable. Their sheer efficacy alone speaks to their reliability, but it's still worthwhile to look into what actually made them reliable.
The main two factors are numbers and profit. First, we know that many people testified to this resurrection. Paul said that Jesus "was seen be over five hundred brethren at once". It's not an accident that he included this number. Five hundred people testifying is a lot. And this isn't new information designed to strengthen an argument - Paul is recapping what he has already told them. Because of this, it's also reasonable to assume that he isn't lying to bolster his claims. It would be far too easily testable for Paul to rest on it if it were false.
The second factor, profit, is actually referring to the complete lack of it. The apostles gained nothing from their ministry. The idea that it might have been a deliberate deception is simply nonsensical. They stood to gain absolutely nothing from it monetarily or socially. In Philippians 1, Paul describes how he rejoices in suffering because it is used to further the gospel, and he condemns those who would preach for reasons other than out of love. And it certainly wouldn't have been a good way to gain the acceptance of their peers: everything they preached was diametrically opposed to the prevailing views of the times. The only explanation for their actions was that to them, "to live is Christ, and to die is gain".
So the early Christians definitely believed in the resurrection of Jesus, and they believed it for good reasons. As I said before, this has pretty major implications for us. The willingness of the apostles to suffer for what they believed, and the belief of the Christians who were not eyewitnesses, indicate a strong historical reliability for the Bible. Given the historical setting, it's not at all reasonable to assume that it was some kind of deception. No one stood to gain from their actions or beliefs at the time.
So, why did the early Christians believe that Jesus was the Son of God? Well, they believed it because He was raised from the dead - which corresponded with the claims He made about Himself while He was alive. And they believed He was raised from the dead because they had numerous reliable eyewitness testimonies about it.
One final question. Why do I believe that Jesus is the Son of God? Well, I believe it because He died for me, and was raised from the dead. And I can know that because the early church died for Him, knowing beyond a doubt that He would then raise them from the dead.