God is the very life of your soul as the soul is the life of your body. That’s the point St. Thomas makes in quoting St. Augustine. (All of St. Thomas is really only an enormous elaboration and explanation of St. Augustine, especially his most famous saying, “Thou hast made us for Thyself, and (therefore, that’s why) our hearts are restless until they rest in Thee.”) The point is simple: Your body isn’t happy without your soul. A body without a soul is a corpse. And your soul isn’t happy without God. A soul without God is a spiritual corpse, a zombie. There are real zombies: spiritual zombies, not physical zombies. Jesus came to earth to save the zombies. Jesus died so that He could put life—His life—into your soul.
–Peter Kreeft, Practical Theology: Spiritual Direction from St. Thomas Aquinas
