What is sin? And what is the "ancestral sin"?

The Orthodox nuance

First, what sin is. The ancient Greek word literally means "missing the mark," like an arrow that misses the target. Sin is not just "I broke a commandment," it is that I turned my back on the One I was made for. And since He is life, breaking away from Him brings, slowly, death. That is why sin is not so much a crime to be punished, as a wound that gets infected.

Now, the delicate part, and here Orthodox Christians speak differently than many in the West. In the West, after Blessed Augustine, the idea solidified that we all inherit Adam's guilt, that we are born already guilty. Orthodoxy does not say this. We say that we inherit the consequences of the fall, a weakened nature, subject to death and easily inclined toward evil, but not Adam's personal guilt. A newborn baby is guilty of nothing.

Why does it matter? Because it changes everything in how you view baptism, man, and God. We do not baptize because the baby is a little culprit who deserves condemnation, but because we want to graft him early onto Christ, to heal him from the beginning of the disease of death and make him a member of the Church. God does not start from "you are guilty," but from "you are sick and I want to heal you."