Well, a big reason to why they are happy is because they trust Jesus. Trusting in Jesus is kind of like trusting a parachute when you know you're going to have to jump out a plane (which in this analogy is death). You know the parachute is there to save you.
But Jesus is not only there for you, but He loves you.
As for accepting the word of God, your past doesn't matter. But also you can't just "accept" it, exactly, you have to truly believe it.
Also, I advise not getting "religious" per say. Hear me out. Jesus didn't like religion either, which, as the Son of God, seems a bit strange, right? Well, religion can be corrupted by man, as can be seen by the ones who falsely accused Jesus and got Him put to death were the religious ones that refused to accept that Jesus was the One they were waiting for because He didn't do what they wanted Him to do.
Many Christians consider it to be a relationship with Christ.
and one thing to remember is, Christians are saved **not** by any work we do. There's nothing we can do to earn our way to Heaven. We have lied, stolen, lusted, hated, and more. And perfect judge (God) can't justly let that go. But that's why Jesus died on the cross. He voluntarily came down to earth, to be beaten, spit on, mocked, whipped, forced to carry His own execution device to His execution spot, where He was nailed to and hung on the cross.
Not for "us" but for **you**. Each person individually. By name. Why? Because He loves us still, no matter how many times we turn our back on Him.
Christ paid the debt for our sins that we couldn't. He takes our sins from our past, present, and future, and paid them on the cross.
Christians just believe Him, repent (which is to confess to God and turn away from our sins) and accept that free gift His has provided for us. We are saved by grace (of God) through faith (in Christ).
