Albert Barnes on 1 Corinthians 15:11

Therefore whether it were I or they. I or the other apostles. It is comparatively immaterial by whom it was done. The establishment of the truth is the great matter; and the question by whom it is done is one of secondary importance.

So we preach. So we all preach. We all defend the same great doctrines; we all insist on the fact that the Lord Jesus died and rose; and this doctrine you all have believed. This doctrine is confirmed by all who preach; and this enters into the faith of all who believe. The design of Paul is to affirm that the doctrines which he here refers to were great, undeniable, and fundamental doctrines of Christianity; that they were proclaimed by all the ministers of the gospel, and believed by all Christians. They were, therefore, immensely important to all; and they must enter essentially into the hopes