[Cronos]

"though you were slaves of sin, you became obedient from the heart to that form of teaching to which you were committed, and having been freed from sin, you became slaves of righteousness. "

Key point, you became i.e. you chose to accept that grace from God to become free from sin. That signifies the free will to chose to accept the grace that saves.

[RnMomof7]

A new heart