Why does a religious person sometimes feel admiration for himself, even though his religiosity is a grace and favor from God that necessitates humility and gratitude?

It is not correct to generalize that religious people are afflicted with the bane of self-admiration (ʿujb), for the Ummah is never devoid of people of truthfulness and humility. One who is self-admiring is not truly among the religious, because sins of the heart are uglier than sins of the limbs. And whoever believes that he is better than others has invalidated his deeds. The bane of self-admiration arises from ignorance, lack of intellect, heedlessness of one's own shortcomings, and focusing on the blessing while forgetting the Bestower. Self-admiration makes its possessor see himself as deserving of reward, and it may lead to his destruction, as the Prophet, peace and blessings be upon him, said: "Three are destructive: stinginess that is obeyed, desires that are followed, and a person's self-admiration." If a person's knowledge is perfected, he will not see any deed as his own, but rather will see it as Allah's enabling grace.