Does Catholic redemptive suffering add to the finished work of Christ?
Robert Sungenis answers that redemptive suffering does not add to the atonement, but Paul says his sufferings fill up what is lacking in Christ's, and the Protestant objection comes from treating justification as a one-time event. He holds, citing Trent's Session 6, Canon 32, that justification is an ongoing process from baptism to death that a Christian increases throughout life.
A viewer asks how to answer Evangelical Protestants who object that the Catholic teaching on redemptive suffering tries to add to the finished work of Christ.
Answer
Paul says in Philippians that by his sufferings he adds to the sufferings of Christ, so it is not that we cannot add to Christ's sufferings and merit from that; Paul is clear that it can happen. What the Protestants confuse is that they think we are adding to the atonement factor required for us to be saved, and that is their mistake, because they believe salvation is a one-time forensic event. If it is a one-time event, then of course you cannot add anything to it, so redemptive suffering would be excluded; you can understand why they ask the question, but it comes from a distorted understanding of justification. The Catholic understanding is that justification is an ongoing process: it starts at baptism and continues throughout your life. As the Council of Trent said in Canon 32 of the sixth session, you increase your justification, a concept totally foreign to a Protestant, who cannot see how you increase a one-time event. Because the Catholic's justification extends from baptism all the way to his death, he adds to it his whole life: his sacrifices, prayers, good deeds, and study all add to it. That is why Paul says he can fill up the sufferings of Christ, because for the Christian it is an ongoing thing.