If God understands my humanity and sin nature better than I do, why does He still hold me accountable for what I cannot help doing?”
A good question. When my children were young, I understood their “humanity and sin” better than they did. Despite this, I held them accountable for their actions because everyone is accountable for their actions. The fact that God understands us better than we understand ourselves is completely irrelevant to whether or not we are responsible for our actions. To be honest, I do not see how you reached the conclusion that we are not responsible for our actions just because God is smarter than we are.
I definitely do not agree that we cannot help what we do. If we agree that we cannot help what we do, then we might as well get rid of our entire legal system. The murderer can say, “I can’t help murdering.” The rapist can say, “I cannot help raping people.” The tax cheat can say, “I cannot help cheating on my taxes” and the adulterer can say to his spouse, “You must forgive me because I cannot help that I had sex with someone else.”
The Bible says in 1 Cor 4:2, “Now it is required that those who have been given a trust must prove faithful.” God has entrusted us with free will to decide how we use our lives. With freedom and free will comes responsibility. That is why we, as humans, believe in justice. God is love and God is justice, and he will hold us accountable for how we use the free gifts he has given us.
By the way, God addresses what is essentially your question in Romans 9:19-25. You might want to check that scripture out.