"What is lacking in the afflictions of Christ"
Anon asked the following:
“St. Paul said, ‘Now I rejoice in my sufferings for your sake, and in my flesh I am filling up what is lacking in the afflictions of Christ on behalf of his body, which is the church.’ How do St. Paul’s sufferings make up for what is lacking in Christ’s afflictions? I thought Christ accomplished all necessary for salvation. St Paul does speak to his audience about their sufferings and how Christ will take it and do ongoing works of salvation. So, is our suffering what St. Paul is talking about as this completion? I don’t understand.”
I referred to this passage (Col 1:24) from St Paul during the summer series talk, “Why Does God Allow Suffering?” I made the point that Christ’s sacrifice on the Cross is the perfect sacrifice, but it is not complete. Yes, Anon, we, the Church, complete it. God allows us to suffer so that, among other reasons, we will complete the afflictions of Christ. We are allowed the incredible gift of sharing in the Cross of Christ so that we will complete it. Elsewhere in his letters, St Paul writes that Christ is the head, the Church is the body. We, as the Body of Christ, complete the suffering of Christ, our Head.
Whenever each of us carries our small portion of Christ’s Cross, our suffering joins in Christ’s work of salvation. This means that our suffering can be salvific; hence, the phrase, “offer it up”. God gives us the opportunity to offer our suffering up for (the salvation of) others in the same way that Christ offered himself up for the salvation of all.
“in the mystery of the Church as his Body, Christ has in a sense opened his own redemptive suffering to all human suffering. In so far as man becomes a sharer in Christ's sufferings—in any part of the world and at any time in history—to that extent he in his own way completes the suffering through which Christ accomplished the Redemption of the world” (“Salvifici Doloris”, Pope John Paul II, 1984).
“If then you are among the members of Christ, whatever human being you are, whoever you are that hears this, whoever you are that does not hear this (but if you are among the members of Christ you do hear this), whatever you suffer at the hands of those who are not among the members of Christ was lacking to the sufferings of Christ.
Your sufferings are added because they were lacking. You fill up a measure, you do not pour something that overflows. You suffer as much as needed to be added from your sufferings to the total suffering of Christ, who suffered as our head, and suffers in his members, that is, in ourselves.
Each one of us in his own measure pays his debt to what may be called this commonwealth of ours. In proportion to our store of strength we contribute as it were a tax of suffering. The final reckoning of all suffering will not take place until the world has come to an end” (St. Augustine).