You foolish man,
do you want evidence that faith without deeds is useless?
I love it when a Bible author just throws it out there like that. He has laid it out, and if you really think about this passage so far, it makes great sense. Still the author knows that there will be those who doubt this. There will be those lazy gluttons who think that they can have faith without works. That they can be true believers, yet be followers of self.
You fools. Is it so difficult to see?
Paul states in Philippians 1:6 that we are to be confident, "...that He who began a good work in you will perform it until the day of Jesus Christ." This salvation that we claim is truly and accurately a work of God.
Be glad though, that the author does go on to offer more explanation. Though the doubting is foolish, he still presents the evidence.