the mystery of the calling of the Gentiles into the Christian Church, so designated in Ephesians 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 Corinthians 15:51), and other doctrines which need to be explained, but which cannot be fully understood by finite intelligence (Matthew 13:11; Romans 11:25; 1 Corinthians 13:2); the union between Christ and his people symbolized by the marriage union (Ephesians 5:31-32; compare 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.”