It's obvious that this mysterious plan of God to unite Jew and Gentile into one Body, the Church, was even hidden from the unseen world of demonic activity. What Paul is saying is that God shouted a message of Triumph to the devil and all his forces that they failed to stop God's plan on having a family of humanity that would bring God glory all over this world!! Now, I know I'm including some theology that isn't immediately apparent in these two verses, but let's remember that Satan sought to destroy God's plan. Satan introduced sin into this plan but God overruled Satan's scheme by sending His Son to die for the lost. God then made it possible for the lost to be saved through Christ and become one Body of people who would bring God glory all over this world. You see the repetition here? What God planned in the Garden of Eden He finished in the Garden of Gethsemane! When Christ rose from the dead God could save all who came to Him through Christ.
As verse 11 says, this was God's eternal plan which was accomplished through Christ Jesus. God was declaring to Satan, "You lost!" God was shouting that He accomplished His plan and will bring it to completion with the Millennial Kingdom of Christ on this earth. And we will be there!!