Carson, below is the common way that Col. 1:24 is interpreted. The afflictions are Christs because he is the head of the church and His body, the church gets afflicted. This is not in regards to his personal bodily afflictions. His bodily giving was complete because He shed His blood. Anyway, we are partners (your term) as ones who share the message of His ultimate affliction. Our afllictions don’t add to His, but are given for the sake of His. I believe there is a difference in what we are saying though it may be that we are not that far apart either.
Geneva SB says: 1:24 Who now rejoice in my sufferings for r you, and fill up s that which is behind of the afflictions of Christ in my flesh for his body's sake, which is the church:
(r) For our profit and benefit.
(s) The afflictions of the Church are said to be Christ's afflictions, by reason of that fellowship and knitting together that the body and the head have with one another. And this is not because there is any more need to have the Church redeemed, but because Christ shows his power in the daily weakness of his own, and that for the comfort of the whole body.
J,F, and B say: 24. Who--The oldest manuscripts omit "who"; then translate, "Now I rejoice." Some very old manuscripts, and the best of the Latin versions, and Vulgate, read as English Version. To enhance the glory of Christ as paramount to all, he mentions his own sufferings for the Church of Christ. "Now" stands in contrast to "I was made," in the past time (Col 1:23).
for you--"on your behalf," that ye may be confirmed in resting solely on Christ (to the exclusion of angel-worship) by the glorification of Christ in my sufferings (Eph 3:1).
fill up that which is behind--literally, "the deficiencies"--all that are lacking of the afflictions of Christ (compare Note, see on 2Co 1:5). Christ is "afflicted in all His people's afflictions" (Isa 63:9). "The Church is His body in which He is, dwells, lives, and therefore also suffers" [VITRINGA]. Christ was destined to endure certain afflictions in this figurative body, as well as in His literal; these were "that which is behind of the afflictions of Christ," which Paul "filled up." His own meritorious sufferings in expiation for sin were once for all completely filled up on the Cross. But His Church (His second Self) has her whole measure of afflictions fixed. The more Paul, a member, endured, the less remain for the rest of the Church to endure; the communion of saints thus giving them an interest in his sufferings. It is in reference to the Church's afflictions, which are "Christ's afflictions, that Paul here saith, "I fill up the deficiencies," or "what remain behind of the afflictions of Christ." She is afflicted to promote her growth in holiness, and her completeness in Christ. Not one suffering is lost (Ps 56:8). All her members have thus a mutual interest in one another's sufferings (1Co 12:26). But Rome's inference hence, is utterly false that the Church has a stock treasury of the merits and satisfactions of Christ and His apostles, out of which she may dispense indulgences; the context has no reference to sufferings in expiation of sin and productive of merit. Believers should regard their sufferings less in relation to themselves as individuals, and more as parts of a grand whole, carrying out God's perfect plan.
In Christ,
Brian