MYSTERY—the calling of the Gentiles into the Christian Church, so designated (Eph. 1:9, 10; 3:8–11; Col. 1:25–27); a truth undiscoverable except by revelation, long hid, now made manifest. The resurrection of the dead (1 Cor. 15:51), and other doctrines which need to be explained but which cannot be fully understood by finite intelligence (Matt. 13:11; Rom. 11:25; 1 Cor. 13:2); the union between Christ and his people symbolized by the marriage union (Eph. 5:31, 32; comp. 6:19); the seven stars and the seven candlesticks (Rev. 1:20); and the woman clothed in scarlet (17:7), are also in this sense mysteries. The anti-Christian power working in his day is called by the apostle (2 Thess. 2:7) the “mystery of iniquity.”
Easton, M. G. (1893). In Illustrated Bible Dictionary and Treasury of Biblical History, Biography, Geography, Doctrine, and Literature (p. 484). Harper & Brothers.