6:16-20 Every man is the servant of the master to whose commands he yields himself; whether it be the sinful dispositions of his heart, in actions which lead to death, or the new and spiritual obedience implanted by regeneration. The apostle rejoiced now they obeyed from the heart the gospel, into which they were delivered as into a mould. As the same metal becomes a new vessel, when melted and recast in another mould, so the believer has become a new creature. And there is great difference in the liberty of mind and spirit, so opposite to the state of slavery, which the true Christian has in the service of his rightful Lord, whom he is enabled to consider as his Father, and himself as his son and heir, by the adoption of grace. The dominion of sin consists in being willingly slaves thereto, not in being harassed by it as a hated power, struggling for victory. Those who now are the servants of God, once were the slaves of sin.
17. But God be thanked, that ye were the servants of Sin—that is, that this is a state of things now past and gone.
but ye have obeyed from the heart that form of doctrine which was delivered you—rather, "whereunto ye were delivered" (Margin), or cast, as in a mould. The idea is, that the teaching to which they had heartily yielded themselves had stamped its own impress upon them.