This really refers back to the charge that the apostle Paul was not an apostle, one of the things the false teachers said about him. Our translation is perhaps not quite strong enough.
In our Protestant exegesis of the Scripture, often this verse is used as one of the arguments to show that Peter was never the Pope, the prime apostle because others were equal with him and chief with him in the work and so was Paul. There was no primacy there for Peter but that is by the way.