vv. 20-21 No distrust made Abraham waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, being fully convinced that God was able to do what he had promised.
In all the talk about faith being what saves us rather than works (following the law), we do have to take care not to turn faith into a work itself. That immediately turns into talk of whether we have "enough" of it or not. You know, "If I had enough faith, then..."
Faith itself is a gift of God. Paul is clear about that. God is doing all the work here, we just have to move with it.
Paul says that Abraham did not distrust. That may be seeing the story through rose-colored glasses. The promise was long in coming for Abraham and Sarah and they must have doubted from time to time whether it was really possible. The story itself in Genesis hints at this reality. Paul does too, when he speaks of Abraham "growing" in faith, in confidence.
I know I distrust, and I know you do too. We're human beings. It's in our nature. But faith is in our nature too in that it is a gift from God, and we can grow in it. One of the ways Paul suggests that we can do so is by worship. "He grew strong in faith as he gave glory to God." That brings me back around to something I've said before, that faith is primarily a communal act, as is worship. When my faith wavers I have yours to hold on to. You can do the same with mine when you need a boost. We are to one another part of that gift of God that is faith. Together we can grow in faith as we "give glory to God." Together we always have enough faith.