Translation
which [is] the mystery that He made known to me by way of a revelation, just as I have written before
Go to footnote numberin a very small way,
Paraphrase
that gracious activity being the heretofore concealed truth which He made clear to me through a supernatural revelation, and which I touched on briefly already,
Footnotes
1
When did Paul write to them before about this? He is most likely referring to statements he made earlier in this very letter about the acceptance of the Gentiles, see 1:9-14 and 2:11-22.