21 What is, “I knew not”? “As it were a beast I became to You, and I am always with You”. There is a great difference between this man and others. He became as it were a beast in longing for earthly things, when being brought to nothing he knew not things eternal: but he departed not from his God, because he did not desire these things of demons, of the devil. For this I have already brought to your notice. The voice is from the Synagogue, that is, from that people which served not idols. A beast indeed I became, when desiring from my God things earthly: but I never departed from That my God.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)