(CG 3/114). That it was necessary for a Law to be given to Man by God (Book 3. God, the End of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THE end which God intends is Himself.

2. The end of every human creature is to adhere to God, for in that his happiness consists.

4. That should be the main purpose of a law, from which the law derives its efficacy. But the law given by God has efficacy among men from the fact that man is suited to God. This therefore ought to be the chief precept in the divine law, that the human mind should adhere to God.

Hence it is said: And now, Israel, what does the Lord your God ask of you but that you fear the Lord your God and walk in his ways, and love him and serve the Lord your God with your whole heart and your whole soul? (Deut. x, 12.)