In his letters, the apostle Paul often uses the word mystery to describe the good news about Jesus (some translations use the word secret). Sometimes, Paul uses mystery as a way of referring to the good news itself (Colossians 2:2; 4:3; 1 Corinthians 2:1; Ephesians 1:9; 6:19). Often, as in Colossians 1:26, Paul says, it is "the mystery that was hidden for ages and generations but is now revealed" (see also Romans 16:25; 1 Corinthians 2:7; Ephesians 3:9). Paul does not mean the good news is a mystery that has to be investigated. He also does not mean the good news is a Gnostic idea that only a few people can understand. (Gnostics emphasized special secret knowledge as the key to salvation.)
Instead, Paul adapts the term from Jewish apocalyptic teaching. The term apocalyptic comes from a Greek word meaning “uncovering” or “revelation.” This is the same word that gives the book of Revelation its name. In the apocalyptic view, God has already created a plan for all of history. This plan exists in God's mind but remains hidden from humans until God chooses to reveal it. For Paul, this secret plan has now been shown to everyone through Christ. It is now being shared throughout the world by his apostles.
In the Old Testament, prophets shared parts of the good news, but God kept some details hidden until the New Testament. These include:
the full participation of gentiles (non-Jewish people) as fellow heirs with Jews (Colossians 1:27; Ephesians 3:1–9);
the indwelling of Jesus Christ in believers (Colossians 1:27; 2:2); and
the union of Christ and his church (this union is shown or illustrated by the union of husband and wife (Ephesians 5:32).
Some parts of God's plan remain hidden and will be revealed in the future, such as:
the salvation of all Israel (Romans 11:25–27); and
Christians will be transformed when Jesus returns (1 Corinthians 15:51–53).
Passages for Further Study
Romans 11:25; 16:25; 1 Corinthians 2:1, 7; 15:51; Ephesians 1:9; 3:1–9; 5:32; 6:19; Colossians 1:26–27; 2:2; 4:3