God’s ultimate plan is to unite all things in Him, in heaven, and on earth. We see this wonderfully explicated in Revelations 21, when Jesus will come back to make all things new. I love that Paul uses the word mystery here because even though God’s plan to rescue and restore us is evident throughout the Bible, it is still very much a mystery. It reminds me of a phrase I heard growing up in the Catholic Church. After communion, the priest says, “Let us proclaim the mystery of faith,” and then we would sing these words, “Christ has died, Christ is risen, Christ will come again.” This, to me, is the epitome of the riches of God’s grace. That Jesus came for us, died for our sins, and will come again to restore all things. Praise be to God!
"7 In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace, 8 which he lavished upon us, in all wisdom and insight 9 making known to us the mystery of his will, according to his purpose, which he set forth in Christ 10 as a plan for the fullness of time, to unite all things in him, things in heaven and things on earth."
Ephesians 1:7-10