All of humanity had been fully identified with Adam. Who he was and what he did became who we are. When we became Christians, God took us out of Adam and placed us in Christ so that we are fully identified with him; who he is and what he did is now ours. We are so identified with him that God sees us seated with Christ on his throne in heaven.
6 and raised us up with Him, and seated us with Him in the heavenly places, in Christ Jesus,
7 in order that in the ages to come He might show the surpassing riches of His grace in kindness toward us in Christ Jesus—(Eph 2:6-7).
Why did he do this? He did this so that he has a basis for showering amazing kindness on us through the ages forever. We are to be an exhibit to the universe of the amazing grace of God. Out of love for us and the desire to glorify his Son, God has given us an amazingly wonderful future.