Does the presence of a personal psychological or material interest in one's work compromise sincerity, such as choosing a lower-paying job for its ease and one's fondness for it, or raising one's son to memorize the Quran in exchange for worldly demands? And does this contradict sincerity by seeking worldly gain through acts intended for the afterlife?

Sincerity is contradicted by intending other than Allah through an action for a corrupt purpose. However, seeking Allah's Countenance and His reward does not contradict the intention of legitimate interests, such as making things easier for oneself and encouraging acts of obedience in a way that aligns with the Lawgiver's intentions. For religion is ease. This includes motivating a child to memorize the Qur'an with worldly promises while also informing him of the Qur'an's virtue and Allah's reward, and reminding him of the Hereafter. The Salaf initially sought knowledge with intentions that were not purely sincere, then knowledge led them to sincerity.