I trusted in Christ for the forgiveness of my sin.
Then I started growing up into righteous works AS A RESULT.
If I had not started that growth, I would be showing myself to not really have received the forgiveness of God. But so many are sure their fruitless, dead faith is indeed the faith that somehow saved them and prepared them for the day of judgment. And they get very defensive and angry and dogmatic if you dare suggest otherwise.
And I think the important point is (after forgiveness of sins)
"Growing up into righteous works as a result"
Growing up and growing in maturity.
Now if we do not see growing up or works (and we need to be very very careful here when making a judgement call here, unless it's purely blatant of course, and even if it is)
We need find out what is going on and why.
If it becomes apparent that someone has said the sinners prayer but has no intention of change then time to wipe the dust of your feet.
However if someone has the will to change but is struggling for what ever reason then it's time to buy a new pair of sandals and walk with them.
Jesus spent 3 years on earth doing that and spent the last 2000 years doing it as well.