19 Expel, therefore, from your hearts carnal thoughts, that you may be really under grace, that you may belong to the New Testament. Therefore is life eternal promised in the New Testament. Read the Old Testament, and see that the same things were enjoined upon a people yet carnal as upon us. For to worship one God is also enjoined upon us. “You shall not take the name of the Lord your God in vain” is also enjoined upon us, which is the second commandment. “Observe the Sabbath day” is enjoined on us more than on them, because it is commanded to be spiritually observed.
For the Jews observe the Sabbath in a servile manner, using it for luxuriousness and drunkenness. How much better would their women be employed in spinning wool than in dancing on that day in the balconies? God forbid, brethren, that we should call that an observance of the Sabbath. The Christian observes the Sabbath spiritually, abstaining from servile work. For what is it to abstain from servile work? From sin. And how do we prove it? Ask the Lord. “Whosoever commits sin is the servant of sin.” Therefore is the spiritual observance of the Sabbath enjoined upon us.
Now all those commandments are more enjoined on us, and are to be observed: “You shall not kill. You shall not commit adultery. You shall not steal. You shall not bear false witness. Honor your father and your mother. You shall not covet your neighbor's goods. You shall not covet your neighbor's wife.” Are not all these things enjoined upon us also? But ask what is the reward, and you will find it there said: “That your enemies may be driven forth before your face, and that you may receive the land which God promised to your fathers.” Because they were not able to comprehend invisible things, they were held by the visible.
Wherefore held? Lest they should perish altogether, and slip into idol-worship. For they did this, my brethren, as we read, forgetful of the great miracles which God performed before their eyes. The sea was divided; a way was made in the midst of the waves; their enemies following, were covered by the same waves through which they passed: and yet when Moses, the man of God, had departed from their sight, they asked for an idol, and said, “Make us gods to go before us; for this man has deserted us.”
Their whole hope was placed in man, not in God. Behold, the man is dead: was God dead who had rescued them from the land of Egypt? And when they had made to themselves the image of a calf, they offered it adoration, and said, “These be your gods, O Israel, which delivered you out of the land of Egypt.” How soon forgetful of such manifest grace! By what means could such a people be held except by carnal promises?
Source: Tractates on the Gospel of John (New Advent)