Colossians 1:27 "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:"
This teaches that Jesus Christ is inside the Born Again man. It is such a mystery that a sinless Saviour would dwell within our wicked bodies. Every Christian should consider this mystery and realize that Jesus should be King over our body, not ourselves. This thought should also keep us from sinning knowing that He is inside us. Every believer has two natures, the flesh and the spirit.
Ephesians 5:32 "This is a great mystery: but I speak concerning Christ and the church."
Ephesians 3:1 "For this cause I Paul, the prisoner of Jesus Christ for you Gentiles, 2 If ye have heard of the dispensation of the grace of God which is given me to you-ward: 3 How that by revelation he made known unto me the mystery; (as I wrote afore in few words, 4 Whereby, when ye read, ye may understand my knowledge in the mystery of Christ) 5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit;"
This mystery tells us that anyone who is saved is in the Body of Christ, which is the Bride of Christ (Rev. 21:9). After the Rapture and the Judgment Seat of Christ, the Body of Christ, who is the Bride will meet her Bridegroom Jesus Christ at the Marriage Supper of the Lamb (Rev. 19:9). Right now, the Body of Christ is called a chaste virgin (2 Cor. 11:2) because the marriage has not yet happened. Although the marriage has happened spiritually already (1 Cor. 6:17), it has not happened bodily (2 Cor. 5:6-8).
Romans 11:25 "For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in. 26 And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: 28 As concerning the gospel, they are enemies for your sakes: but as touching the election, they are beloved for the fathers' sakes. 29 For the gifts and calling of God are without repentance. 30 For as ye in times past have not believed God, yet have now obtained mercy through their unbelief:"
This mystery deals with the blindness of Israel as a nation and their restoration in the future during the Millennium. The mystery revealed is that God is not through with Israel. God will take the wandering Jews and bring them back to Palestine, which He has already done and convert them to Jesus Christ during the Tribulation. They will then get all of their land back in the Millennium.
1 Corinthians 15:51 "Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, 52 In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. 53 For this corruptible must put on incorruption, and this mortal must put on immortality. 54 So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory. 55 O death, where is thy sting? O grave, where is thy victory?"
This mystery deals with the disappearance of the Body of Christ at the end of the Church Age, before the Tribulation. There will be two types of people that go up in this rapture, the saved dead and the saved that are still alive. The saved will get glorified bodies and go up to meet Jesus and it will happen "in a moment, in the twinkling of an eye."