“if I, brothers, still preach circumcision” – Apparently the Galatians had heard that Paul still preached circumcision (“still” as in “as he did before he was converted”). It seems that the one who was troubling the Galatians about circumcision had claimed Paul was preaching the same thing. The legalists had actually used Paul’s name to try to give their message authority, but Paul reckons if he was preaching circumcision, then people wouldn’t be persecuting him, because the offensive part of the gospel would’ve been removed.
We’re familiar with the fact that people find certain Christian beliefs offensive (e.g. regarding marriage), and some people seem to take pride in the fact that people are offended by their “Christianity”, but I don’t think that’s what Paul’s talking about here, and I think people are entitled to get annoyed when Christians (or people who claim to be Christians) display a “holier than thou” attitude. That’s not why Paul was being persecuted.
He says he could’ve avoided persecution by preaching religion. The people he has in mind who find the cross offensive are people like you and me, who tick all the right religious boxes. We’ve been going to the right church for years, we don’t get drunk, we don’t sleep around, we read our Bibles, we pray.
Sermons about how Christians should behave appeal to us, either because we feel like we’re doing pretty well compared to those drunkards out there, or because we like being challenged to work even harder so we’ll be able to feel good about ourselves later, but the cross says none of that stuff counts. Not that it’s not important – we’ll come onto that later: don’t use your freedom as an opportunity for the flesh – but it doesn’t count (v6).
Paul was persecuted because he wouldn’t allow people to think they could add their own efforts to what Christ did for our justification. The offence of the cross is that all that religiosity that people are so proud of is like filthy rags.
Instead, God wants to give us righteousness as a free gift to glorify his son who paid for our sin on the cross.