God is just. Someone needs to pay the price for our sin. Can you pay the price for your sin by doing good deeds? No. If you were driving and went through a red traffic light, you won't be able to make it up by stopping at the next few traffic lights. You'd need to pay a monetary fine. We are so helpless we cannot do more than good deeds. But good deeds are what we are required to do. In fact, failing to do a good deed is a sin.

James 1:23-27

For if anyone is a hearer of the word and not a doer, he is like a man who looks intently at his natural face in a mirror. For he looks at himself and goes away and at once forgets what he was like. But the one who looks into the perfect law, the law of liberty, and perseveres, being no hearer who forgets but a doer who acts, he will be blessed in his doing. If anyone thinks he is religious and does not bridle his tongue but deceives his heart, this person’s religion is worthless. Religion that is pure and undefiled before God the Father is this: to visit orphans and widows in their affliction, and to keep oneself unstained from the world.

So we need to pay for our rebellion against God. As every sin is a rebellion against God. And the punishment for that is death- eternal separation from the one we rebelled against.

But God is merciful and loving. This is why God became Man, lived the life we should have lived and died the death that we deserved, paying the punishment as an infinite sacrifice and payment for our sins, so we may be forgiven.