Since when has the mystery been hidden?
Scripture says the mystery, or secret, has been hidden from the beginning of the world, or the age. It was hid in God, the sovereign God who created all things by Jesus Christ. This was according to His prerogative to keep things secret.
Les explains from Ephesians that Paul was to make all men see the fellowship of the mystery, or secret, which from the beginning of the world, or the age, has been hid in God. It was not merely hidden among Israel or the Gentiles but was hid in God, the sovereign God who created all things by Jesus Christ. Les emphasizes that it is God's prerogative to keep things secret if He wants to. The surrounding context also notes that God had the Gentiles on His mind, though under different circumstances, and that aspects of the mystery include Israel's spiritual blinding for almost two thousand years and the Gentiles coming into a privileged position with Israel's God in the body of Christ.
And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ: