1QpHab 7
Commentary on Habakkuk... and God told Habakkuk to write down that which would happen to the final generation, but He did not make known to him when time would come to an end. And as for that which He said, That he who reads may read it speedily: interpreted this concerns the Teacher of Righteousness, to whom God made known all the mysteries of the words of His servants the Prophets. For there shall be yet another vision concerning the appointed time. It shall tell of the end and shall not lie. Interpreted, this means that the final age shall be prolonged, and shall exceed all that the Prophets have said; for the mysteries of God are astounding. If it tarries, wait for it, for it shall surely come and shall not be late. Interpreted, this concerns the men of truth who keep the Law, whose hands shall not slacken in the service of truth when the final age is prolonged. For all the ages of God reach their appointed end as he determines for them in the mysteries of His wisdom. Behold, [his soul] is puffed up and is not upright. Interpreted, this means that [the wicked] shall double their guilt upon themselves [and it shall not be forgiven] when they are judged ... [But the righteous shall live by his faith].
Ephesians 3:3
1 For this reason I, Paul, the prisoner of Christ Jesus for the sake of you Gentiles 2 if indeed you have heard of the stewardship of God’s grace that was given to me for you, 3 that by revelation the mystery was made known to me, as I wrote before briefly. 4 When reading this, you will be able to understand my insight into the mystery of Christ 5 (which was not disclosed to people in former generations as it has now been revealed to his holy apostles and prophets by the Spirit), 6 namely, that through the gospel the Gentiles are fellow heirs, fellow members of the body, and fellow partakers of the promise in Christ Jesus.
Notes and References
"... Attempts have been made at times to trace the Pauline idea of mystêrion to Paul's Hellenistic background. True, in the rites of some mystery religions of the time the initiate was brought into relationship with the deity through a vision (epopteia) and was assured of salvation (sötêria) through the protection of the deity. In Pauline writings, however, the idea of mystêrion bears only a superficial verbal resemblance to such Hellenistic ideas, since the content of his mystêrion is quite different ... For Paulit denotes a secret hidden in God for ages and now made known to humanity in Christ Jesus that the salvation available to human beings comes through Christ; it shares in the apocalyptic character of euangelion, 'gospel' ... it is this notion of mystery that has again turned up in the Qumran literature. In the commentary on Habakkuk we read, apropos of Hab 2:2 ... Here one sees rz mcaning something hidden in God that is now made known; in this idea one finds the parallel to Paul's mystêrion. The content of the 'mystery' is different. In the Qumran commentary it refers to the hidden meaning of God's words to the prophet Habakkuk, whereas in Pauline theology the content of the mystery is Christ and his role in salvation now made known. What is the same in both the Qumran and the Pauline usage is the idea of mystêrion or rz as a carrier, whereas the content or what is carried is different ..."
Fitzmyer, Joseph A. According to Paul: Studies in the Theology of the Apostle (pp. 27-28) Paulist Press, 1993