A MYSTERY — but emphatically not a puzzle or something unknowable. In Paul it is an OPEN SECRET: something long hidden in God and now announced, whose content he states plainly at Ephesians 3:6 — that Gentiles are fellow heirs, in the same body. ⚠ This is nearly the opposite of the word's use in the Hellenistic MYSTERY-RELIGIONS, where a mystērion was what initiates must never reveal; Paul's mysteries are precisely the things now published. The Latin Vulgate sometimes rendered it sacramentum, which is how 'mystery' and 'sacrament' came to be entangled in Western theology. ⚠ Mark uses the same word in nearly the opposite direction: at Mark 4:11, the mystērion of the kingdom is given to the Twelve alone, singular, while 'those outside' get only parables — a mystery still functioning as something kept, not yet the published, everyone's-mystery sense Paul will later give the word. Matthew's parallel (13:11) makes it plural, mystēria, a small but real difference this library does not harmonize away. → first discussed at Ephesians 1:9