that is, the mystery made known to me by revelation, as I have already written briefly.
Verse 3. How that by revelation. . He refers to the revelation which was made to him when he was called to the apostolic office, that the gospel was to be preached to the Gentiles, and that he was converted for the special purpose of carrying it to them. See . Unto me the mystery. The hitherto concealed truth that the gospel was to be preached to the Gentiles.
I suffer as Christ's prisoner for preaching that the gospel's privileges belong to believing Gentiles no less than Jews. Though the world condemns me and cast me into prison, Christ owns His servants in their suffering; faithful ministers must dispense His sacred truths, however disagreeable to some, whatever the cost to themselves.
AI summary
Commenting on Ephesians 3:1-13
he made known--The oldest manuscripts read, "That by revelation was the mystery (namely, of the admission of the Gentiles, Eph 3:6; Eph 1:9) made known unto me (Gal 1:12)." as I wrote afore--namely, in this Epistle (Eph 1:9-10), the words of which he partly repeats.