22 “For I am prepared for the scourges”. Quite a magnificent expression; as if He were saying, “It was even for this that I was born; that I might suffer.” For He was not to be born, but from Adam, to whom the scourge is due. But sinners are in this life sometimes not scourged at all, or are scourged less than their deserts: because the wickedness of their heart is given over as already desperate. Those, however, for whom eternal life is prepared, must needs be scourged in this life: for that sentence is true: “My son, faint not under the chastening of the Lord, neither be weary when you are rebuked of Him.” “For whom the Lord loves He chastens, and scourges every son whom He receives.” Let not mine enemies therefore insult over me; let “them not magnify themselves;” and if my Father scourges me, “I am prepared for the scourge;” because there is an inheritance in store for me. You will not submit to the scourge: the inheritance is not bestowed upon you. For “every son” must needs be scourged. So true it is that “every son” is scourged, that He spared not even Him who had no sin. For “I am prepared for the scourges.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)