Every human being has some sort of gospel. It is in our nature to justify the wrong we have done, and to do so by whatever means necessary so as to ease our conscience. For many, it's the "bookkeeping" gospel -- adding up all the credits and debits, weaving it out so they end up in the black, and there you have it: a free pass into Heaven. Don't break any of the bigger commandments like killing or adultery, don't swear too often, and don't speed within city limits.
Here's how N.D. Wilson puts it:
"The laws of God are viewed as a series of French pane windows, and if you get through your life without breaking most of them, then God will receive you. But James tells us that the law of God is one great big plate glass window, and James says that if you break it anywhere, you broke the whole window. It doesn't matter if you heaved a brick through the middle of it or out a few BB holes in just one corner. 'For whoever shall keep the whole law, and yet stumble in one point, he is guilty of all' (James 2:10)."
Man is all about how they come out on the weigh scale. As long as the good outweighs the bad, you're good.
But God is the only one who can cancel sin -- mine and yours. We cannot justify ourselves, like Arcade Fire said, "Do you think your righteousness could pay the interest on your debt?" The answer is no. Only Jesus can save. God told Adam in the garden, "The day that you eat of [the fruit], you shall surely die" (Genesis 2:17).
Ezekiel says, "The soul who sins shall die" (Ezekiel 18:20). Paul says, "The wages of sin is death" (Romans 6:23).
When a man "in the black" dies, his good does not atone for the penalty -- this is the penalty. It is the natural consequence of sin and not the thing which "balances" it.
In order to have true atonement, to truly come into the black, a sinless man had to die for sinful men.