Who now rejoice. — In the true reading of the original there is no relative pronoun. The sentence starts with emphatic abruptness, “Now (at this moment) I rejoice” (just as in 2 Corinthians 7:9). In all the three Epistles of the Captivity this same rejoicing is declared in himself and urged on his brethren. In Ephesians 3:13, “I desire that ye faint not at my tribulations for you, which is your glory;” in Philippians 2:11, “Yea, if I be offered upon the sacrifice and service of your faith, I joy, and rejoice with you all. For the same cause do ye also joy, and rejoice with me.” There, as here, the rejoicing is in suffering, not in itself, not solely because it is borne with and for Christ, but also because it is for the sake of the Church. Here, however, this idea is expressed with far greater emphasis.
Fill up that which is behind of the afflictions of Christ. — The sense of this passage is at first sight startling, but it could not have been thought difficult or doubtful, had not false inferences from it tempted men to shrink from the obvious meaning. Now, (1) the “afflictions of Christ” is a phrase not used elsewhere; for “affliction” (properly, hard and galling pressure) is the ordinary burden of life, and is generally spoken of only as coming on His servants. But, like the common phrase “the sufferings of Christ” (2 Corinthians 1:5; Philippians 3:10; 1 Peter 4:15; 1 Peter 5:1), it must moan the afflictions which He endured. It is true, as has been thoughtfully suggested (see Chrysostom and others on the passage) that we are to count as His the afflictions of His Church; but still, even if we are to include these indirect afflictions, we cannot possibly exclude the direct. Next, (2) St. Paul expressly says (in the full force of the original) that “he fills up instead” of his Master, what is still left unfinished of his Master’s afflictions. (See the passages quoted by Dr. Lightfoot in his note on this verse.) He declares, i.e., that, succeeding to the suffering of Christ, he carries it out for the sake of His body the Church. This is, indeed, nothing but a clearer and more striking expression of the truth conveyed in 2 Corinthians 1:5, “The sufferings of Christ overflow to us,” so that we bear our part, in addition to the full measure which He bore; and even in the commoner expression, to be “partaker of Christ’s sufferings” (Philippians 3:10; 1 Peter 4:13), or “to drink of His cup and be baptised with His baptism” (Matthew 20:22-23). But, (3) looking to the meaning and use of the word “afflictions,” we note that “the afflictions of Christ” must be His sufferings on earth considered simply as a part — though immeasurably the chief part — of the burden of humanity in a sinful world, They represent, not the Cross of Atonement, on which He alone could suffer — and in which any reader of St. Paul must find it absurd to suppose that he would claim the slightest share — but the Cross of struggle against sin even to death, which He expressly bade us “take up if we would follow Him.” This He has still left “behind;” this in His strength every one of His servants bears, partly for himself, partly also for others. In the former light St. Paul says, “The world is crucified to me, and I to the world” (Galatians 6:14); in the latter he claims it as his highest privilege “to fill up that which is behind of the afflictions of Christ for His Body which is the Church.”
In my flesh for his body’s sake. — There is obviously an antithesis here. St. Paul suffers in his natural body for the mystical Body of Christ.