What does it mean that the law is not of faith?
It means the law is based on doing, not believing. Scripture says the law is not of faith; the one who does them must live in them. Justification is not by law but by faith plus nothing, because keeping the whole law is impossible without temple, priesthood, and sacrifice.
Les explains that the law is not of faith because it operates on works rather than believing. The context quotes Galatians: the just shall live by faith plus nothing, and the law is not of faith, but the man that doeth them has to live in them. So if a person seeks salvation by law-keeping, they must keep it all, to the last iota. A new believer illustrated this by saying that to keep the law you would need a temple, a priest, and a herd of sheep. Les agreed, noting that even with a temple, priesthood, and sacrifice, they could not accomplish it, because it is impossible. Thus the law demands perfect doing, while righteousness comes by faith.
And the law is not of faith: but, The man that doeth them shall live in them.