Who now rejoice in my sufferings for you, and fill up those things that are wanting of the sufferings of Christ, in my flesh, for his body, which is the church ( Colossians 1: 24).
This passage cannot be interpreted in the sense that there was any deficiency in the redemptive sufferings of Christ. No, rather the sufferings of Our Lord were of infinite value and could have redeemed any number of possible men.
What, then, does Saint Paul mean here? We must first affirm the doctrine of the communion of saints in the Mystical Body. When we suffer “through Him, with Him, and in Him” as members of His Body our sufferings in grace (indeed all our good works and prayers) benefit the other members of the Church, both Militant and Suffering in Purgatory. This is what Saint Paul’s sufferings are “filling up.” As members of His Body we are channels of His grace.
Recall the words of Our Lord concerning the Day of Judgment and how He applied them to those on His left and His right. To the blessed sheep the Good King says:
“Come, ye blessed of my Father, possess you the kingdom prepared for you from the foundation of the world. For I was hungry, and you gave me to eat; I was thirsty, and you gave me to drink; I was a stranger, and you took me in: Naked, and you covered me: sick, and you visited me: I was in prison, and you came to me.Then shall the just answer him, saying: Lord, when did we see thee hungry, and fed thee; thirsty, and gave thee drink? And when did we see thee a stranger, and took thee in? or naked, and covered thee? Or when did we see thee sick or in prison, and came to thee? And the king answering, shall say to them: Amen I say to you, as long as you did it to one of these my least brethren, you did it to me.” (Matthew 25:35-41)
And to the condemned wicked, the goats, He repeats the same only that they did not do these things for their neighbor or, through them, to Him.
Other commentators note that the words of Saint Paul could also apply not to the Passion of Christ but to His three years of public labor wherein He could not do all things; in fact, Jesus told His disciples that they would do “greater things” than even He Himself did: “Amen, amen I say to you, he that believeth in me, the works that I do, he also shall do; and greater than these shall he do” (John 14:12).
In a commentary by Father Charles Jerome Callan there is found another light on this text, that from the Greek Fathers. I quote: “But the Greek Fathers explain it otherwise. Admitting that the passion of our Lord was entirely sufficient to save all mankind, they hold that its fruits are not applied to all except through the sufferings of the saints; and hence what is “wanting of the sufferings of Christ” is their application through the trials and tribulations which the Apostles and the faithful endured and continue to endure for Christ’s sake and in union with Him.”
I hope that the passage is now more understandable. It was for me, as I have been more or less ignorant of the meaning for a long time.