Paul used the Greek word musterion six times in his letter to the Ephesians. This word musterion is most often translated mystery in our English Bible. But this can be a little misleading. To us mystery connotes something esoteric, unknowable, or that cannot be understood. However, the Greek word musterion means something that one could not know until it is revealed, a secret revealed, a religious or mystical truth that is only known by those initiated in the religion.
Musterion could more accurately be translated as sacred secret. A truth that is unknowable until God reveals it, which he did through Christ. We believers have this mystery, or sacred secret, revealed to us. Furthermore, God has called us to make this sacred secret known to all people. We, like Paul, have been chosen “to make plain to everyone the administration of this mystery, which for ages past was kept hidden in God” (Ephesians 3:9). Paul reiterates his message in verse 10 just to make sure we got it. [God’s] intent was that now, through the church (that’s us), the manifold wisdom of God should be made known.
Or, in other words, our mystical calling in Christ is to know him and make him known.
* No, I’m not referring to the South Park character Mysterion or Professor Satchafunkilus and the Musterion of Rock, both of which Google thinks I should be much more interested in than a translation of the Greek word musterion.