All this may refer to what Paul has written in verses 14, 16, and 17, but more likely refers to verse 17 only, that is, to God’s work in the new creation.
From God is a literal translation. Good News Translation gives the correct sense, “done by God.” In languages where the passive form is difficult or unnatural, translators will probably want to turn the sentence around to say “it is God who has done all this.” But this may also require that it be a separate sentence, or it may require the use of a colon to introduce the following statement.
Us: as in verse 16, it is not clear whether Paul is referring to all Christians, to himself and his companions, or to himself only (so Moffatt and An American Translation, but not Parola Del Signore: La Bibbia in Lingua Corrente) in verses 18-19. Since “we” and “you” are distinguished in verse 20, it seems best to assume that Paul is not including the readers in verses 18b-19. But it is difficult to imagine that Paul would have wanted to exclude his readers from the first us having to do with being reconciled with God.
Who through Christ reconciled us to himself: Christ is the means through which God reconciled sinners to himself. Though Paul does not here say explicitly “through the death of Christ,” the context (verses 14-15) and parallel passages (Rom 5.10) show that through Christ means “through his death.”
Paul does not use the verb “to reconcile” or the noun “reconciliation” very often in his letters, but see Rom 5.10. These words are metaphors from the realm of personal relations in which enemies have become friends again. In 1 Cor 7.11 it is used of reconciliation between husband and wife. Implicit in the idea of reconciliation is that the people who are reconciled were previously enemies. Good News Translation makes this explicit: “changed us from enemies into his friends.” For Paul it is not God who was our enemy; rather we were the ones who were opposed to God (see Rom 5.10-11). Note that Barclay uses the term “friendship” throughout this section, while Contemporary English Version draws on the image of “peace.”
Ministry of reconciliation: the word rendered ministry may also be translated “work” or “service” (diakonia; see comments on 3.7; 4.1). Contemporary English Version fills out the meaning with “the work of making peace between himself and others.” The same idea may be expressed “the work of bringing other people back to God” (Good News for the World) or “the task of helping others to accept that friendship” (Barclay).
Quoted with permission from Omanson, Roger L. and Ellingworth, Paul. A Handbook on Paul’s Second Letter to the Corinthians. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .