The Importance of Repeating Advice to Those Who Do Not Attend the Congregational Prayer

If a person knows men who do not attend the congregational prayer, and he knows that they have already been advised by others, is his conscience cleared by that?
His conscience is not cleared. If you know that a person is committing a forbidden act or neglecting an obligatory one, and he has been advised by someone else but was not successful in complying, it is obligatory for you to advise him. This is because he may accept it from you but not from the other person. Also, the one who advised him first may have approached him with harshness, while you approach him with gentleness. The acceptance of gentleness is clear, so he may accept it from the second person but not from the first.