William Burkitt on Romans 6:20

That is, you were free de facto, not de jure; when you were sin's servants, you were void of righteousness, that had no part of your service then; therefore sin should not have on joy of your service now; as righteousness had no part of your service in your carnal state, so there is no reason why sin should have any service from you in your gracious state.

Learn, That such sinners as are now become servants to God, ought to be as free from sin, as before they were free from righteousness: It will evidently appear so, if we consider the great and good Master which we serve, the nature of our present work, the certainty and transcendency of our future reward, the obligations we lie under as creatures, as new creatures, by the law of creation, by the favour of redemption, by the promise and hopes of glorification; all this should engage us to the love and practice of universal holiness.