St. Thomas Aquinas: On the Soul is a Christian Meditation Book For Kindle, which I hope will help you better understand the theology of St. Thomas Aquinas.
While asking questions about the nature of man, St. Thomas spends some time reflecting upon the characteristics of the soul[1] or soul; he divides his inquiry into seven questions. In these eight questions, he investigates all of the general questions regarding the essence, potency’s and relationship of the soul or soul.
Q1
Aquinas first shows that the soul’ essence is not its substance, since that belongs to God alone. God’s essence and operation are one. Can we speak of the soul as having an essence? Are there potencies in the soul? The soul or soul is still a creature, since all creatures receive their substance from another. The soul is no different from any other creature, yet it is of the highest sense a creature, since it soul’s the body. If the soul had life actually, it would not depend upon another for its potency; but it actually does receive its potency from another. The soul has life apart from the body. It does not need the body for its existence. The soul is subsistent.