“[ὅτι] κατὰ ἀποκάλυψιν ἐγνωρίσθη μοι τὸ μυστήριον, καθὼς προέγραψα ἐν ὀλίγῳ, πρὸς ὃ δύνασθε ἀναγινώσκοντες νοῆσαι τὴν σύνεσίν μου ἐν τῷ μυστηρίῳ τοῦ Χριστοῦ,” — Ephesians 3:3, 4.

“and how the mystery was made known to me by revelation, as I wrote above in a few words, a reading of which will enable you to perceive my understanding of the mystery of Christ.” — Ephesians 3:3, 4 NRSV.

The reference to the “mystery” (μυστήριον) of Christ refers us back to Ephesian 1:9ff: “…he has made known to us the mystery of his will, according to his good pleasure that he set forth in Christ, as a plan for the fullness of time, to gather up all things in him, things in heaven and things on earth.” (NRSV.) I’ve always thought μυστήριον would be better translated “secret” here rather than “mystery.” It signifies something previously unknown which has now been revealed. Translating it as “mystery” suggests it is obscure or hidden, but Ephesians proclaims the μυστήριον has now been revealed. God’s intentions in Christ were unknown before, but now revealed.