In the first chapter of Ephesians, Pau; lays out what it means to be in Christ.
First is that God is now dealing in grace and peace opposed to wrath. Then we see where our blessings are and how they will be realized.
Next we see how we have those blessings: by being in the one who was chosen before the foundation of the world. Our position of being adult children is brought out through the adoption, further explained in Galatians 4.
We are now accepted in Christ before God. This is because of the redemption we have through the blood of Christ. Now we know the mystery of His will, having the completed word of God. We have an eternal inheritance in Christ when we trust in his finished work on the cross.