The ultimate explanation for what the Trinity is doing is simply love. It is not more complex than that. God finds enjoyment and affection for us that many times if not all the time we find hard to understand. But Ephesians tells us that God's plan is motivated by personal love for his own.
In love
5 He predestined us to adoption as sons and daughters through Jesus Christ to Himself, according to the kind intention of His will, (1:4-5).
He predestined us to adoption as mature sons and daughters who enjoy the privilege of being loved the way the Father loves the Lord Jesus Christ. When you hear the word adoption, Ephesians is not referring to the adoption of a baby but the adoption of a full grown adult into a family with the full privileges of that family. Out of love, God has determined that we should not be second-class citizens in heaven but well-loved sons and daughters.
