Now to him who is able to establish you in accordance with my gospel, the message I proclaim about Jesus Christ, in keeping with the revelation of the mystery hidden for long ages past, but now revealed and made known through the prophetic writings by the command of the eternal God, so that all the Gentiles might come to the obedience that comes from faith — to the only wise God be glory forever through Jesus Christ! Amen.
The gospel that Paul calls his own is that which he preaches and teaches. It is a gospel each of us can call our own. It becomes ingrained in us and is part of our very being. The good news of Jesus Christ is our reason for existence. It is the message we each proclaim with every word we speak and every action we take.
The revelation that Paul speaks of is truth that has been revealed by God, not by human wisdom. No man could come up with this plan for salvation. Only the God of creation.
Verse 25 might be better rendered as "the mystery kept silent through times eternal." It is written in the perfect tense, meaning that it is permanent. It isn't something that happened was fully revealed, but a mystery that has been partially revealed to us. God's fullness is not made known to humanity, but the message of salvation through Jesus Christ is now revealed to everyone.
The prophets wrote of it under the direction of God, but no one understood what it meant until its revelation was made known through Jesus Christ. This was only done by God's command, not by anything that humanity had done. His sovereignty is always in place. He decides the world's fate and commands things to happen in his time.
His command had a purpose, to bring all of the Gentiles into obedience through faith.
He is wisdom and in Him we glory through Jesus Christ.
Amen.