The law of faith... Faith in Whom? This, naturally, should become the follow up question to what you asked. If we are under a 'law of faith', then who exactly started this law?
If we look at the passage you quoted, it seems to indicate that the law we are not under is the Mosaic law. Hence the comment about God not being a God of the Jews only. This can only make sense if He was referring to the law that was given only to the Jews.
Now, who is it that we are putting our faith in? Of course, Jesus is that person. When we put our faith in Jesus, we are doing the same thing that the Israelites did with the Mosaic law. We say," If I abide by these rules, then I am right with God." The same is said with Jesus and His rules. WHAT?? Jesus has rules/commands? Yes, He does. The famous sermon on the mount contains 70% of them, and the rest are found in the rest of the four gospels.
If we want to be under this 'law of faith', then we must do as Paul did and start following the Lamb (Jesus) wherever He goes.
In peace