'Mystery' in the Bible

Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints:

To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory:

That their hearts might be comforted, being knit together in love, and unto all riches of the full assurance of understanding, to the acknowledgement of the mystery of God, and of the Father, and of Christ;

Withal praying also for us, that God would open unto us a door of utterance, to speak the mystery of Christ, for which I am also in bonds:

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