'Mystery' in the Bible

that is, the mystery which was hidden [from angels and mankind] for ages and generations, but has now been revealed to His saints (God’s people).

God [in His eternal plan] chose to make known to them how great for the Gentiles are the riches of the glory of this mystery, which is Christ in and among you, the hope and guarantee of [realizing the] glory.

At the same time pray for us, too, that God will open a door [of opportunity] to us for the word, to proclaim the mystery of Christ, for which I have been imprisoned;

that I may make it clear [and speak boldly and unfold the mystery] in the way I should.