Have you been thinking all along that we have been defending ourselves to you? It is in the sight of God that we have been speaking in Christ, and all for your upbuilding, beloved. ESVUK

Ultimately, Paul was living ‘for an Audience of one.’ He spoke ”in the sight of God”. He wasn’t trying to justify himself to them. It certainly seems like Paul has been defending himself in this letter. It feels as if he had to. But in the most important sense he did not need to defend himself to them. They were not his judge and jury. Paul understood God to be his only Judge, and he was countering the attacks against him ”in the sight of God”.

Also, in the spirit of true parenthood, his speaking was in order to be helpful to them.

‘The reason he has worked hard to counter lies about him, Paul writes, is for their sake, in order to build them up. He calls them his beloved. He has been waging this war of words in order to persuade them that what he taught them about Christ is trustworthy and true. He doesn’t want them to be led away from Christ and into sin by these false teachers. If he needs to stand up for himself in order to save them, he will do it.’ BibleRef