"But now Christ has been raised from the dead, the firstfruits of those who have fallen asleep. For since death came through a man, the resurrection of the dead also comes through a man. For as in Adam all die, so also in Christ all will be made alive." -- 1 Corinthians 15:20-22
When I was at PyCon, I hung out with @jacobian, @brainwane, and some others while they were painting their nails. The subject turned to religion, and I quickly realized as a person who wasn't a secular humanist, I was a bit of an outlier.
When asked, I began talking about some of what's in the Bible. Jacob asked, "So, you believe the things in the Bible actually happened?" I said "yes." The conversation didn't last long afterwards...we were interrupted by something, I forget what. But given that it's Easter, I'd just like to expound a bit on how that idea is relevant to Christ's resurrection.
The attitude I see a lot of humanists have towards religion is, "Hey, believe whatever you want, so long as it makes you a better person." In their eyes, the goal of religion is to make people better able to follow the shared moral code. The doctrine doesn't matter.
Christianity doesn't hold to that idea. We believe that the ethical code we follow isn't a set of rules that God made up just because He felt like it. Rather, it's derived from the character of God Himself. And breaking that ethical code isn't just bad because it hurts ourselves, or even those around us. It actually separates us from God.
God is love, and mercy, and He is willing to forgive...but more than anything else, He is holy. And part of holiness is that evil just cannot exist in His presence, and He cannot let any evil go unpunished. Even the theoretically minor evil of yelling at the guy who just cut you off on the freeway.
Our problem, then, is that we need someone else to take the punishment for our evil. And that's what Jesus did on Good Friday. For the three hours of darkness while He was hanging on the cross, He was suffering the wrath of God the Father. When He died, the payment for our sins was completed. And when He rose again, He was showing us that even though we will still die physically, those who follow Him will be restored to life.
That's why we believe the Bible so strongly. Jesus' death wasn't just a nice story about atonement, it was the atonement itself. If Jesus didn't actually suffer for our sins and die, then we have no reason to believe that our sins are actually paid for. And if Jesus didn't actually return to life afterwards, then we have no reason to believe that we will return to life after our death.