Not all cessation from a sin is the mortification of it. A man may forsake one harlot and fall in with another.
This is why preaching moralism instead of gospel leads to MORE lostness and not less.
Satan will gleefully relent from tempting you in a lesser sin if it means you fall into the greatest sin of pride. The abstention from a sin can itself be rooted in sin.
This is why the gospel is so central to Christianity and what makes it unique. The Pharisees (and the Elder Brother in the parable of the Prodigal) were not lost by their visible sins, they were lost because of their damnable good works.
All other religions are essentially advice. (Do this. Don’t do that. Earn your reward.)
The gospel is essentially just news. (Jesus did it. You didn’t. Receive Jesus’ reward.)