Looking back on everything he has written thus far, Paul says his defense of himself is really intended to “upbuild” (ESV) the church. Paul considers his letter to be a legal defense against an attack coming from his opponents in Corinth. He describes it as an apology in the legal sense of the word (ἀπολογέομαι). Acts 24:10 uses the word for Paul’s legal defense before Felix, the Roman governor. Paul has been defending himself, but not for the purpose of winning the argument with the church and proving himself to have been in the right all along. His goal in this defense is to build up the church in Christ.
The word Paul uses is used for buildings or structures (οἰκοδομή), the ESV uses the odd word “upbuild” the NIV has “strengthening,” the KJV has “edifying.” Paul uses this metaphor frequently to refer to things that “build up” the church in contrast to tearing down the church (1 Cor 14:12, spiritual gifts, 14:16, orderly worship). In Romans 15:2 it refers to speech which “builds up” a neighbor.
Paul has used architectural metaphors in 1-2 Corinthians several times (the temple of the Holy Spirit, etc.) Sometimes to construct something new old things must be destroyed. Old structures need to be demolished and the ground needs to be properly prepared for a new structure to be built. Edification therefore requires Paul to occasionally knock down old ways of thinking (especially the pagan worldview of the Corinthian church) before he can build up the church to maturity.
If the church felt they had been wronged by Paul or they were offended by his change in plans, it was because their suspicions about Paul were wrong or the accusations coming from the opponents were wrong. Paul’s defense in the last few chapters was to allay their fears so that their anger with Paul will no longer hinder their maturity in Christ. If Paul has hurt the church, it is because it as necessary to tear down their existing ways of thinking in order to replace those structures with a Christ-like world view.
This is a very difficult aspect of ministry to get right since most people in the church feel attacked if a pastor tries to deal with tough issues from the pulpit. I think Paul has it right, he preaches Christ crucified seeks to apply the death and resurrection to all aspects of life. In my experience, preaching through the text of the the Bible will raise issues in context churches need to hear.
To a large extent, any pastor who is leading a congregation needs to worry less about their reputation or legacy than the spiritual growth of their congregation. A pastor who is seeking to pad out a resume for the next (bigger and better) church has completely missed the point of being a servant of Jesus Christ.