11 “Be sure that the Lord He is God”. Who knows not that the Lord, He is God? But He speaks of the Lord, whom men thought not God: “Be sure that the Lord He is God.” Let not that Lord become vile in your sight: you have crucified Him, scourged Him, spit upon Him, crowned Him with thorns, clothed Him in a dress of infamy, hung Him upon the Cross, pierced Him with nails, wounded Him with a spear, placed guards at His tomb; He is God. “It is He that has made us, and not we ourselves.”
It is He that has made us: “and without Him was not anything made that was made.” What reason have ye for exultation, what reason have ye for pride? Another made you; the Same who made you, suffers from you. But ye extol yourselves, and glory in yourselves, as if you were created by yourselves. It is good for you that He who made you, make you perfect....“We are His people, and the sheep of His pasture.” Sheep and one sheep. These sheep are one sheep: and how loving a Shepherd we have! He left the ninety and nine, and descended to seek the one, He brings it back on His own shoulders ransomed by His own blood. That Shepherd dies without fear for the sheep, who on His resurrection regains His sheep.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)