(Answering just this part, but acknowledging you said much more.)
The same way you can be saved with faith -- God!!! God saves. God gives faith. Not this complicated. God gifts a whole bunch. He gifts us with justification, grace, forgiveness, love, hope, ability to do his good. He even keeps gifting us. Gifts us with knowledge, wisdom, the ability to do services for our bros, healing, teaching, prophecy, etc. etc.
And he gives us even more -- love joy, peace, forbearance, (okay, so maybe neither one of us has that one in great supply, but we have some), kindness, goodness, and self-control.
God isn't stingy. He gives more than one thing to us!
I just looked up the gifts and the fruit God gives us and excluded one word two times -- Faith!
I didn't use that word, because you already thought you had that gift to become saved. But, I have to ask, if that was there to become saved, then why does he keep having to give us the same thing again?
Personally, I consider faith something like a US Savings Bond. In the tradition of my family, each child was gifted with one of those at birth. It costs half-value of what it would mature to become. Can't faith be like that? Something we get a little of at birth, and matures the longer we follow the Lord, so it grows as we grow?