Matthew Levering speaking at Wheaton College - a brief audio excerpt of a lecture on St Thomas Aquinas on the Decalogue. Link to audio on iTunes and at Wheaton as Mp3. The text of Aquinas's Explanation of the Ten Commandments is available at the Dominican House of Studies priory site here.
These are the ten precepts to which Our Lord referred when He said: “If you would enter into life, keep the commandments” (Mt 19:17). There are two main principles of all the Commandments, namely, love of God and love of neighbor. The man that loves God must necessarily do three things: (1) he must have no other God. And in support of this is the Commandment: “You shall not have strange gods”; (2) he must give God all honor. And so it is commanded: “You shall not take the name of God in vain”; (3) he must freely take his rest in God. Hence: “Remember that you keep holy the Sabbath day.”
But to love God worthily, one must first of all love one’s neighbor. And so: “Honor your father and mother.” Then, one must avoid doing harm to one’s neighbor in act. “You shall not kill” refers to our neighbor’s person; “You shall not commit adultery” refers to the person united in marriage to our neighbor; “You shall not steal” refers to our neighbor’s external goods. We must also avoid injury to our neighbor both by word, “You shall not bear false witness,” and by thought, “You shall not covet your neighbor’s goods” and “You shall not covet your neighbor’s wife.”