The popular concept that a mystery is something mysterious or secret tends to obscure the fact that it is not used in this way in Scripture. In the NT the word refers to divine truth which is now revealed after being hidden from men in OT days. It appears 27 times.
In Matt. 13:11 Christ began to reveal “the mysteries of the kingdom of heaven,” a series of truths having to do with the previously undisclosed period between His first and second comings. The church age is a mystery “kept secret since the world began,” Rom. 16:25, but made known to the apostles, Eph. 3:1-12. This revelation makes it clear that Israel cannot be identified with the church.
Other NT mysteries include the change in believers at the translation of the church at the end of the age, 1 Cor. 15:51, 52; 1 Thess. 4:13-17; the mystery of the church as the bride of Christ, despite the fact that He is also Israel’s Messiah, Eph. 5:23-32; the mystery that Christ dwells within believers, Gal. 2:20; Col. 1:26, 27; the mystery of God in Christ, 1 Cor. 2:7; Col. 2:2, 9; the mystery of the gospel, Eph. 6:19; the mystery of godliness, 1 Tim. 3:16; the mystery of God’s purposes in “the dispensation of the fullness of times,” Eph. 1:9-12; the mystery of Israel’s present blindness, Rom. 11:25; the mystery of iniquity, 2 Thess. 2:7; the mystery of the seven stars, Rev. 1:20; the mystery of Babylon, Rev. 17:5, 7.
William Evans, The Great Doctrines of the Bible, (Chicago: Bible Institute Colportage Assoc., 1912), WORDsearch CROSS e-book, 306.
AMEN.