Atheists are always saying that sin is just a man-made concept created in the Bible to
keep the masses in line. Let's see if that's true. Take the Ten Commandments, for example.
Let's pretend they didn't tell us to stay away from sin and said the following:
1. Thou shalt cheat on your spouse whenever possible.
2. Thou shalt steal anything you want.
3. Thou shalt murder anyone that gets in your way.
4. Thou shalt not have to work if you don't want to.
5. Thou shalt neglect your kids if they're too much trouble.
6. Thou shalt abort your babies if they're inconvenient.
7. Thou shalt cuss out your parents if they don't know what's up.
8. Thou shalt take drugs, even if it endangers your health.
9. Thou shalt neglect education if studying is too bothersome.
10. Thou shalt fight others to show how big and bad you are.
Oh, wait! That's right! We ALREADY do those things. And just look at the state of the
world.
Sin is not a man-made concept. Sin is any destructive urge that Satan -- whose power is death by deception (John 8:44, Hebrews 2:14) -- has made attractive by way of illusion (which is why lust, violence, pride, laziness, greed, etc, all feel so good and then lead to trouble. You may have noticed this effect in your own life a few times). This is why God does not allow sin in his kingdom. In fact, he explains in a few places in the Bible (1st Corinthians 5:6, Galatians 5:9) that even a little sin starts to destroy everything around it.
Sin separates us from God, and that's a bad thing, considering that God is the one by whom all things consist and are maintained by:
(Colossians 1:17)
And he is before all things, and by him all things consist.
Considering that God has given our souls the ability to live forever, how long do you think it would take us to die, should we depart from him? Forever?
We can't atone for our own sins because these fallen, carnal bodies of ours can't stay away from sin any more than a scarecrow can stay away from straw. Sin is practically what we're made of. When Adam and Eve believed Satan's lie that man didn't need God and could become like God by his own hand (Genesis 3: 1-6) our very bodies were cursed (Genesis 3:19) and we were thereafter born into an incarnation of sin. When man believed Satan's lie he gave himself a death penalty and THAT is why Jesus had to die on the cross in our place. Our first covenant that gave us life had been broken and Jesus made a new one on our behalf (Which is why it's called the New Covenant, or New Testament.)
Without accepting his new covenant and letting it cover us we are still subject to that death penalty. It's an endless, eternal departure from the only one who can give us life. It's proper name is hell, and it is very real.
(Matthew 10:28)
And fear not them which kill the body, but are not able to kill the soul: but rather fear him which is able to destroy both soul and body in hell.