If the Corinthians realize that Christ is in them, then they will have proof that Paul is a true apostle, for he was the one who brought them to faith in Christ (1 Cor 4.15)!

I hope: in 1.13 and 5.11 this same word is used to indicate a degree of confidence in the Corinthians, but here it is almost like a command to them to correct their thinking before he comes. However, it would not be appropriate to translate it as a command.

As in verse 4, the pronoun we does not include the Corinthians. And as in verse 4, the pronoun we may be an epistolary plural. If so, translators may wish to say “that I have not failed” (so Nueva Biblia Española, and similarly An American Translation, Moffatt, and Parola Del Signore: La Bibbia in Lingua Corrente).

That we have not failed: this continues the image of testing pointed out in the previous verse. Where possible the same kind of terminology should be used to show this relationship.

In the context of this letter, the words find out that we have not failed mean that Paul hopes the Corinthians will realize that he has proven himself to be a true apostle (see 12.11-12). The verb may be rendered “discover” (Contemporary English Version), “come to know” (Anchor Bible), or “come to recognize” (New Jerusalem Bible).

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 .