I’m sure it’s obvious to lots of people. And I’ve had suspicions along this direction for a while. But looking at it more closely I’m now convinced that 2 Cor 5:11-6:13 is primarily about establishing Paul’s apostolic authority.
5:11-15 discusses the apostolic ministry, motivated by the fear of God and the love of Christ. In the light of which, no-one should be regarded in a “fleshly” way (5:16). In the light of what Paul has been saying in 2 Corinthians thus far, this can reasonably be seen as referring both to converted individuals and to ministries. Converted individuals have a brand new life in Christ, which cannot be seen yet (5:14-15). Authentic ministers will look unimpressive on the outside, but inwardly speak the word of the creator God that brings new life. Look at a converted individual or an authentic minister according to the flesh, you will see the wrong thing. People are doing just this with Paul.
5:17 gives the right way to see things. A new creation is being brought about. Yes, metaphorically individuals are being made new, dying and rising to new life (5:14-15). But also a new cosmos is created at the death and resurrection of Christ, one that those “in Christ” have already entered.
How this comes about (5:18-19) is through Christ’s reconciling work (cf. “died for all, 5:14-15), and through the message of reconciliation. The effective coupling of those two makes for a ministry of reconciliation.
Therefore, how are we to regard the apostles, if it is not to be according to the flesh? The answer is “as ambassadors for Christ”. They are those through whom God makes the appeal to be reconciled.
There are two startling things about the appeals to “be reconciled to God” and to open up their hearts to Paul (6:13). 1. They are addressed to the Corinthian Christians. They are not an evangelistic appeal, but something that the Corinthians need to do. 2. They bracket 6:1-10. The pragmatic value of an exposition of Paul’s ministerial suffering is an appeal to open their hearts to Paul and to be reconciled to God.
So this passage is not primarily an evangelistic message about how the unbelieving world can be reconciled to God, although it has massive implications along those lines. Instead, Paul wants the Corinthians to understand his vital place, alongside Christ, in reaching the world with reconciliation. The Corinthians are not reciprocating Paul’s affections towards them. They are not valuing his ministry. That means that, although believers already, they are putting themselves beyond God’s ministry to reconcile himself to all peoples. Paul is so important in God’s mission, as ambassador of reconciliation, that the Christian who has started to devalue Paul needs to be implored afresh to be reconciled to God.
Paul Barnett, NICNT 2 Corinthians, page 301:
“This entire apologia (2:14-7:4) has been necessitated by Corinthian doubts about Paul’s apostolicity in view of serious opposition and criticism of him in Corinth. Paul’s twofold appeal (“Be [you] reconciled to God. ... [You] do not receive the grace of God in vain” – 5:21; 6:1) is directed specifically to the Corinthians. Their doubts about Paul as an apostle are tending to place them outside God’s saving purposes. Hence Paul’s powerful reminder, “Behold, now is the time of [God’s] favor… the day of salvation.” To align themselves with the eschatological purposes of God, they must first accept Paul’s place in the divine scheme of things.”