Albert Barnes Commentary Romans 6:18

"and being made free from sin, ye became servants of righteousness." — Romans 6:18 (ASV)

Being then made free from sin. That is, as a master. You are not under its dominion; you are no longer its slaves. They were made free, as a servant is who is set at liberty, and who is, therefore, no longer under obligation to obey.

Ye became the servants, etc. You became voluntarily under the dominion of righteousness; you yielded yourselves to it; and are therefore bound to be holy. Comp. See Barnes "John 8:32".