14 “He shall drink of the brook in the way, therefore shall he lift up his head”. Let us consider Him drinking of the brook in the way: first of all, what is the brook? The onward flow of human mortality: for as a brook is gathered together by the rain, overflows, roars, runs, and by running runs down, that is, finishes its course; so is all this course of mortality. Men are born, they live, they die, and when some die others are born, and when they die others are born, they succeed, they flock together, they depart and will not remain.
What is held fast here? What does not run? What is not on its way to the abyss as if it was gathered together from rain? For as a river suddenly drawn together from rain from the drops of showers runs into the sea, and is seen no more, nor was it seen before it was collected from the rain; so this hidden rain is collected together from hidden sources, and flows on; at death again it travels where it is hidden: this intermediate state sounds and passes away. Of this brook He drinks, He has not disdained to drink of this brook; for to drink of this brook was to Him to be born and to die.
What this brook has, is birth and death; Christ assumed this, He was born, He died. “Therefore has He lifted up His head;” that is, because He was humble, and “became obedient unto death, even the death of the Cross: therefore God also has highly exalted Him, and given Him a Name which is above every name; that at the Name of Jesus every knee shall bow, of things in Heaven, and things in earth, and things under the earth; and that every tongue shall confess that Jesus Christ the Lord is in the glory of God the Father.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)