Now this I say and testify in the Lord, that you must no longer walk as the Gentiles do, in the futility of their minds.
Ephesians 4:17

The primary mark of a true convert is a change in behavior, a discernible repentance from sin. Paul says "must", not "should". God's grace must be accompanied by obedience to his commandments, not because obedience is the price of grace, but because obedience is the only appropriate response to grace.