4 First then let there be laid as a foundation in your soul the doctrine concerning God; that God is One, alone unbegotten, without beginning, change, or variation; neither begotten of another, nor having another to succeed Him in His life; who neither began to live in time, nor ends ever: and that He is both good and just; that if ever thou hear a heretic say, that there is one God who is just, and another who is good, you may immediately remember, and discern the poisoned arrow of heresy. For some have impiously dared to divide the One God in their teaching: and some have said that one is the Creator and Lord of the soul, and another of the body; a doctrine at once absurd and impious. For how can a man become the one servant of two masters, when our Lord says in the Gospels, No man can serve two masters? There is then One Only God, the Maker both of souls and bodies: One the Creator of heaven and earth, the Maker of Angels and Archangels: of many the Creator, but of One only the Father before all ages—of One only, His Only-begotten Son, our Lord Jesus Christ, by Whom He made all things visible and invisible.
Source: Catechetical Lectures (New Advent)