D-R Bible, Haydock Commentary:
Ver. 24. And fill up those things…in my flesh for his body, which is the church. Nothing was wanting in the sufferings or merits of Christ, for a sufficient and superabundant redemption of mankind, and therefore he adds, for his body, which is the church, that his sufferings were wanting, and are to be endured by the example of Christ by the faithful, who are members of a crucified head. See St. Chrysostom and St. Augustine. (Witham) — Wanting. There is no want in the sufferings of Christ himself as head; but many sufferings are still wanting, or are still to come in his body, the Church, and his members, the faithful. (Challoner) — St. Chrysostom here observes that Jesus Christ loves us so much, that he is not content merely to suffer in his own person, but he wishes also to suffer in his members; and thus we fill up what is wanting of the sufferings of Christ. (St. Chrysostom) — The wisdom, the will, the justice of Jesus Christ, requireth and ordaineth that his body and members should be companions of his sufferings, as they expect to be companions of his glory; that so suffering with him, and after his example, they may apply to their own wants and to the necessities of others the merits and satisfaction of Jesus Christ, which application is what is wanting, and what we are permitted to supply by the sacraments and sacrifice of the new law.