This one is a mouthful!
It boils down to this: God is planning to bring everything under the Lordship of Jesus and it gives Him pleasure to include us in this plan!
But let's look in a little more detail:
While God's ways are very much beyond our grasp and ken, He chooses to make this mystery made known to us. And although we only scratch the surface of it, He wants us to begin to know and understand it all.
Paul says "No eye has seen,no ear has heard,no mind has conceived what God has prepared for those who love him -- but God has revealed it to us by his Spirit." (1Cor2:9-10)
And in the Old Testament we read: "He has also set eternity in the hearts of men; yet they cannot fathom what God has done from beginning to end." (Ecc3:11)
Including us in His plan is God's good pleasure. Elsewhere Paul notes that we are God's fellow-workers(1Cor3:9).
And we are in a process, the world is not there yet, times have not yet reached fulfilment yet, but there will be a great and glorious day when every knee will bow and tongue confess that Christ is Lord, and all tears are wiped away!
But in the meantime, God has placed Eternity in our hearts!
Although we don't fully understand, we have His message and the hope of His coming that burns in us. He has entrusted His message into our hands and we are His Fellow-Workers whose greatest reward and longing is to see Jesus crowned over all!
What a blessed privilege!