This dissertation examines the teachings of Thomas Aquinas (d. 1274) and Gabriel Biel (d. 1495) on questions of motivation for Christian activity. What is the proper motivation for loving God and neighbor? Is it acceptable to look to a reward in performing acts of charity? In order to answer these questions, I explore each thinker's understanding of human or voluntary action, merit, the relationship between nature and grace, the role of the divine missions and of habits in moral activity, and what it means for each to love God above all else.This research addresses a void in the scholarship because there is little substantive comparison between Aquinas and Biel. Prior examinations of Biel's reception of Aquinas were mainly concerned with whether Biel accurately quotes or paraphrases him. However, this method provides little insight into their core theological emphases. This dissertation explores many of the controlling insights that influence how each thinker approaches questions of motivation.For Aquinas, it is acceptable—even necessary—to look to a reward while performing acts of charity. In general, Aquinas establishes a non-competitive relationship between self-love and love for God that allows him to claim that the act of charity is spontaneous because it is consistent with the human person's God-given will for self-perfection. For Biel, however, the act of charity cannot include any reference to the good of the human person. God is loved from charity solely for God's goodness ad intrarather than ad extra. By establishing a competitive relationship between self-love and love for God, Biel emphasizes restraint rather than spontaneity in Christian activity.Biel's use of Aquinas on questions of motivation is negligible. Decisive differences regarding the relationship between God and the human good, the role of habits in the Christian life, and each thinker's appreciation for divine transcendence lead to very distinctive takes on motivations for Christian activity. Moreover, a preliminary examination of sixteenth-century debates about motivation reveals that the default position of both Protestants and Catholics seems to be closer to that of Biel than to that of Aquinas.