The third use of the law is only for believers who are already justified and regenerate. Indicatives come before imperatives in a way that maybe in a sermon gospel would not come before law. We think what we're doing is presenting something before people and offering it to them, but God doesn't work that way with words. It's not that faith is a condition for receiving what the gospel teaches, but that the teaching itself as it's being taught as God is proclaiming justification. He's giving us the faith to receive it.