I said nothing about mistakes, improving or religion.
I asked, “Are they sinless?”.
I assume you are referring to Christians being forgiven for their sins by accepting Christ as their savior and of course by your definition they are not sinless.
But your definition has no meaning to an atheist or a Deist like me since we dont believe in the divinity of Christ. So all we can do is live our life a moral as we can. We are human and will make mistakes so all we can do is try to not repeat them. We can not fall back on the crutch of being forgiven.
I know that is hard to comprehend to you as a Christian.
For clarification Atheists do not believe in any god and Deists believe in a creator that created the universe but doesnt actively interfere with it. So a completely different concept than the god of the Bible.
But maybe I am misinterpreting what you are getting at.