--This verse comes in the context of consolation in affliction. Paul's emphasis here is then not on the atonement but on consolation of Christ in the lives of suffering Christians. But Jesus Christ's sufferings here are clearly "for us."
4:8-10 - "We are afflicted in every way, but not crushed; perplexed, but not driven to despair; persecuted, but not forsaken; struck down, but not destroyed; always carrying in the body the death of Jesus, so that the life of Jesus may also be made visible in our bodies."
--Here is a clear statement of participation in Christ's death; it is always "carried in the body" of his servants. "Carrying in the body the death of Jesus" correlates with the sufferings that Paul and his fellow apostles experience and which he described here. Affliction, perplexity and persecution all allow Christians to participate in the death of Jesus Christ.
5:14-21 - "For the love of Christ urges us on, because we are convinced that one has died for all; therefore all have died. And he died for all, so that those who live might live no longer for themselves, but for him who died and was raised for them.
From now on, therefore, we regard no one from a human point of view; even though we once knew Christ from a human point of view, we know him no longer in that way. So if anyone is in Christ, there is a new creation: everything old has passed away; see, everything has become new! All this is from God, who reconciled us to himself through Christ, and has given us the ministry of reconciliation; that is, in Christ God was reconciling the world to himself, no counting their trespasses against them, and entrusting the message of reconciliation to us. So we are ambassadors of Christ, since God is making his appeal through us; we entreat you on behalf of Christ, be reconciled to God. For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God."
-- Many things are going on in this passage, one we can justly call one of the central atonement passages in Paul's letters.
First, Paul insists that since "one has died for all," thus "all have died." It is not immediately clear whether by "all" he means all Christians or all people; v. 15 ("those who live") seems to imply anyone living. I'm sure Five-Pointers have an argument for this passage, but to me it seems to be that Paul is referring to all people.
Second, we have a clear explanation of the purpose of atonement: "that those who live might live no longer for themselves, but for him who died and was raised for them." The (or "a") purpose of the atonement is that we might live for Christ and not for ourselves. The purpose of the atonement is to make us into disciples and followers of Christ.
Third, atonement is tied intimately and essentially, to God's work of redemption and re-creation. "If anyone is in Christ, there is a new creation: everything old has passed away; see everything has become new! All this is from God, who reconciled us to himself through Christ." Atonement has cosmic effects.
Fourth, Green and Baker make the case that God does not need to be reconciled to man but rather man to God; that the problem lies in our affections, not God's. This passage seems to support that view, since it always speaks of man being reconciled to God, never God to man: "God, who reconciled us to himself...God was reconciling the world to himself...be reconciled to God." If God indeed needed to reconcile himself to the world this would have been a perfect place to say so. However, this is an argument from silence and not enough to disprove the objectivity of God.
Fifth, Paul seems to be speaking here not of the how of atonement but of the what. "Reconciliation" does not describe how the atonement effected something, but rather what was effected. Atonement accomplishes reconciliation. I think we can safely conclude from this passage that reconciliation is a, if not "the," key purpose of atonement--mankind reconciled to God, restored to a proper relationship. Such a restored relationship has implication for every facet of life--a human being restored to a right relationship with God is by implication restored to a right relationship with other human beings and with the rest of creation.
Sixth, in this passage we have one of two examples of "status exchange" in Paul (the other being Galatians 3:13-14). Jesus was "made to be sin" so that we might "become the righteousness of God." From a penal substitutionary standpoint, this makes sense: Jesus Christ was "made to be sin" as a substitute for our sins, bearing the weight in himself of God's judgment on sin. For other interpretations this presents a problem: what does it mean that Jesus "became" sin? Indeed, the question of what it means for us to "become" the righteousness of God poses a problem for any interpretive framework. But maybe an understanding of our becoming the righteousness of God can help us interpret the idea of Jesus becoming sin. Of course, the phrase "righteousness of God" has itself many interpretations. Obviously, this is one of the more difficult atonement verses to explicate and one I'll have to return to later.
8:9 - "For you know the generous act of our Lord Jesus Christ, that though he was rich, yet for your sake he became poor, so that by his poverty you might become rich."
--Craig L. Blomberg writes, "Contra some liberation theology, this statement probably does not refer to the material or socio-economic circumstances of Jesus througohut his earthly life. Rather if offers a far more profound theological summary of all that he gave up in leaving his heavnily home for the constrictions of earthly existence and the ultimate ignominy of crucifixion" (1999). This passage deals with atonement as long as atonement is defined as (as I see it) "Christ's work for us." Thus, since Christ's poverty (cf. Philippians 2 and comments here) makes us "rich," in the same spiritual sense of the poverty he embraced, this passage can properly be seen as referring to atonement.
13:4 - "For he was crucified in weakness, but lives by the power of God."
--A simple statement about Christ's weakness in death, followed by a statement of Paul's own weakness "in him." Christ's vindication after a shameful death from which he exercised no power to escape implies vindication for Paul's weakness and our own weakness today. Those who are "in" Christ will have their suffering in weakness vindicated in Christ.Sources:
Blomberg, Craig L., Neither Poverty nor Riches: A Biblical Theology of Possessions. Downer's Grove: IVP; Leicester: Apollos, 1999.