What would happen to us without the grace of God according to this passage?
Without God's grace, we would be no different from those who rejected the knowledge of God and fell for humanist deception and pagan worship. Our old human nature is bent to rebel, and God would give us up to uncleanness, placing us right in the middle of what is described.
Les explains that but for the grace of God, you and I would be no different from these people. They had a knowledge of God through the heavens and from Noah and his sons, yet within a couple of generations they were ready to follow a humanist setting up pagan worship. He says our old human nature is bent to rebel, so without grace we would be right in the middle of what is described in the next verses, including God giving them up to uncleanness. He warns not to look down on them, because by the grace of God they can also be where he is.