Why does God have to speak before a person can have faith?
Faith comes by hearing, so God must first speak and reveal His word before anyone can believe it. Abraham believed God because God had said something to him, and that belief was counted to him as righteousness. Without God's spoken word, there is nothing to hear or trust.
Les explains that the Scripture is what counts—not what Paul says and not what any teacher says, but what God says. He points to Abraham: God said something, and Abraham believed it. That is why faith comes by hearing: God has to say something before mankind can believe it. Abraham's belief was then imputed to him for righteousness. Les also brings in James, verse 21, anticipating the charge that the Bible contradicts itself, and he begins to address that apparent problem.
So then faith cometh by hearing, and hearing by the word of God.