What do you mean by trapped?
And who said he isn't still human?
You said man's nature was altered. Changed to what exactly, animal, machine, alien fish? If man is still human, his nature has not altered, has it? Can he express all that it means to be human when he has a corruption in his flesh and a lack of spiritual life that prevents him from being all that it means to be human ie. made in the image and likeness of God?
Romans 7:24
What a wretched man I am! Who will rescue me from this body that is subject to death?
We are trapped in a hopeless position, spiritually dead with a body of corruption. Grace and truth comes beside us to show us there is hope, there is light at the end of the tunnel (so to speak).
As I understand you, based on what I have read of your posts, you seem to be under the impression that we are by nature born evil. If that were true no-one could be saved. There would be no redemption, evil cannot be redeemed, it can only be destroyed. We are born neither good nor evil for these things are an aspect of our character, not our nature. God alone is good by nature, ie. inherently good. We learn good or evil based on our response to the grace and truth with which God presents to us.
This thread asked the question why do some people believe and others not? It didn't ask why are some saved and some not. Jesus told us the answer, some prefer darkness, some prefer light. The two will never understand each other any more than chocoholics will understand why some don't like chocolate or why some are cat people and some are dog people. We are either believers because we value goodness, righteousness and truth or we are unbelievers because we value self. When did you find out you were a believer? (rhetorical question). There are many in the world right now that think they are unbelievers but, before their life is through, they will find out that's not true. God promised to save believers.