Really good questions and ones that require some consideration.
Someone who doesn't believe in God is likely not to be persuaded by what others hold as Holy Scripture.
May I recommend that you read a book by C.S. Lewis.
It's called Mere Christianity and it spells out in a very simple, logical way Lewis' belief at a base level about not only the existence of God, but in his belief in Jesus as the Son of God.
If these questions about the basis of faith are real, and I believe they are, you might find this book a good insight on how people come to a point of faith from a previous point of atheism, like Lewis did.
Thanks, but I prefer to just ask people this way. That way I don’t have to make assumptions from what I may gain through insight. I could easily be incorrect. Besides, most people don’t like someone saying they believe x because someone read something.