How can one overcome doubts and anxiety concerning Islamic faith when seeing adherents of other religions clinging to their beliefs, especially with the whispering of Satan and the unease caused by the sophistries of Christians?

A person's aversion to demonic whispers (waswas) and evil suggestions (khawatir) is a sign of faith and soundness of belief. Doubt (shakk) is different from waswas; doubt can lead its possessor out of the fold of Islam. The psychological comfort that misguided individuals may feel does not indicate the correctness of their beliefs. The solution lies in turning away from waswas and avoiding dubious matters (shubuhat).