...and to make plain to everyone the administration of this mystery, which for ages past was kept hidden in God, who created all things.
τοῦ μυστηρίου τοῦ ἀποκεκρυμμένου ἀπὸ τῶν αἰώνων ἐν τῷ θεῷ τῷ τὰ πάντα κτίσαντι
Marcion read:
...and to make plain to everyone the administration of this mystery, which for ages past was kept hidden from God, who created all things.
So the sense is clear in a marcionite reading: the demiurge didn't know the mystery.
Now, I would like to question the marcionite reading of the my preferred verses of all the NT, 1 Corinthians 2:6-8:
6 We do, however, speak a message of wisdom among the mature, but not the wisdom of this age or of the rulers of this age, who are coming to nothing. 7 No, we declare God’s wisdom, a mystery that has been hidden and that God destined for our glory before time began. 8 None of the rulers of this age understood it, for if they had, they would not have crucified the Lord of glory.
We are said (surely Stuart may confirm) that Marcion had these verses precisely how they stand now. But what if also there the God who is mentioned is not the Good God but the creator god? In particular, was really a marcionite thing to say the fact that the Good God revealed a hidden mystery (etc etc) for sake of the Christians only now? In other terms, is the predestination a Marcionite thing? My suspicion is that the predestination is more a feature of the creator god, who 'planned' the salvation [=possession of a better knowledge] of some people just when he created the his world.
So a speculative reconstruction may be the following:
6 We do, however, speak a message of wisdom among the mature, but not the wisdom of this age or of the rulers of this age, who are coming to nothing. 7 No, we declare wisdom, a mystery that has been hidden from God before time began. 8 None of the rulers of this age understood it, for if they had, they would not have crucified the Lord of glory.
6 σοφίαν δὲ λαλοῦμεν ἐν τοῖς τελείοις, σοφίαν δὲ οὐ τοῦ αἰῶνος τούτου οὐδὲ τῶν ἀρχόντων τοῦ αἰῶνος τούτου τῶν καταργουμένων·
7 ἀλλὰ λαλοῦμεν σοφίαν ἐν μυστηρίῳ, τὴν ἀποκεκρυμμένην τῷ θεῷ πρὸ τῶν αἰώνων·
8 ἣν οὐδεὶς τῶν ἀρχόντων τοῦ αἰῶνος τούτου ἔγνωκεν, εἰ γὰρ ἔγνωσαν, οὐκ ἂν τὸν κύριον τῆς δόξης ἐσταύρωσαν.
So now the Good God's wisdom is opposed directly to the demiurge's wisdom and his rulers. The sense is the same of original Ephesians 3:9: even before the creation of the his world, the demiurge didn't know the wisdom of the Good God, and so also the his rulers.