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.
18. Being then—"And being"; it is the continuation and conclusion of the preceding sentence; not a new one.
made free from Sin, ye became the servants of—"servants to"
Righteousness—The case is one of emancipation from entire servitude to one Master to entire servitude to another, whose property we are (see on Ro 1:1). There is no middle state of personal independence; for which we were never made, and to which we have no claim. When we would not that God should reign over us, we were in righteous judgment "sold under Sin"; now being through grace "made free from Sin," it is only to become "servants to Righteousness," which is our true freedom.