How can one deal with hard-hearted Muslims who shy away at the mention of anything religious, and who do not accept advice or admonition, and are there positive and effective ways to deal with them?

Hardness of hearts is one of the most dangerous diseases that lead to turning away from the remembrance of Allah, and it is a sign of deprivation. Nevertheless, there is hope for the rectification of those with hard hearts, for hearts are in the hand of Allah; He turns them as He wills.

The داعي (caller to Islam) must not despair of reminding and advising them, using various means such as engaging stories and beneficial news, and he may add some humor that does not compromise dignity. He should also utilize occasions like death and visiting graves to offer advice, and he should be a good role model.