What is the relationship between charity and knowledge in the theology of Thomas Aquinas? Did Aquinas in his mature thought portray charity's act as antecedent to and independent of practical reasoning? Did he view charity's motion as rendering us morally good before God, apart from whether or not we do what is right in our actions? A dominant stream in contemporary Catholic ethics holds for precisely such a concept of charity, and many recent commentators on Aquinas maintain that this is his position as well. According to Michael S. Sherwin however, the contrary is in fact the case. By Knowledge and By Love represents a major contribution to Thomistic moral theology and philosophy by providing a thoughtful examination of Aquinas' psychology of action and his theology of charity. Through a comprehensive analysis of the relation between intellect and will, knowledge and love, and charity and the infused intellectual virtues, Sherwin concludes that, far from divorcing the will from reason, Aquinas in his later works integrates reason and will more closely together. Saint Augustine says, "No one can love what he does not know."

According to Sherwin, Aquinas holds that God's grace respects and elevates this dynamic in the gift of charity, which depends on faith's knowledge, and on the knowledge provided by the other infused cognitive virtues and gifts. Charity is a virtue, and like any virtue its acts require some knowledge of their object. Sherwin argues that not only is this a faithful reading of Aquinas, it also has profound implications for any conception of moral development. The role of a mentoring community, the characteristics of friendship with God, and the specific actions required by love all play a part in Sherwin's analysis.