The purpose of this work is to explore and explain St. Thomas’ curious description of charity as a “kind of friendship of man for God.” This is achieved in two symphonic movements: 1) An investigation into the metaphysical substructure of friendship; 2) Analysis of St. Thomas’ commentary on St. John’s Gospel from which he takes his understanding of charity as friendship. In the first part, basic concepts are defined which are employed ubiquitously by the Angelic Doctor whenever he discusses love and friendship. Once a basic lexicon is built, the author distinguishes diverse kinds of love given the anthropology of St. Thomas. This in term is employed in the specific love of friendship noting also Thomas’ dependence upon the Philosopher, Aristotle. Finally, charity itself is examined based primarily upon Thomas’ treatment in the Secunda secundae of the Summa Theologiae. The second movement of the work engages the text of Thomas’ commentary. Aquinas sees the Incarnation as the archetype of all transformation in Christ, namely, that Christ establishes with man a common life upon which friendship is based. This common life must move from the sensible to the spiritual, from human life to Divine. This course is tracked by the author with special emphasis on the means employed by Christ now with His would-be friends, namely, the gift of His Spirit and the Sacrament of Charity.