Paul explained in Ephesians 3:9-13 that God sent Christ to be the payment for our sins, both Jews and Gentiles. He brought to light the fact that it was God's plan hidden for ages. Not just Jews, but Gentiles who had faith were also saved. And through the church "the manifold wisdom of God might be made known to the rulers and authorities in the heavenly places." Since this is the eternal purpose of God realized in Christ Jesus, we have confidence through our faith in Him.
This was a hard passage to understand and explain. But so far chapter 3 has been about the revelation of the mystery of the gospel. Paul basically explains that the salvation that comes from Christ's death on the cross revealed that the plan of salvation is for all who have faith. Prior to that, Jews believed this salvation was going to be for them only. Ultimately they rejected Christ as their Savior and His death on the cross paid for the sins of all who believe. Of course all is done for God's glory, not ours. And salvation is another way His glory is revealed.
Praise God for His Glory.