Union with Christ is the heart or center of all that has been revealed of God's thought concerning man and of man's relationship to God. Union with Christ is like the hub of a mighty wheel. There are many spokes to that wheel - election, creation, redemption, salvation, sanctification, glorification; and then, like a series of subsidiary spokes - repentance, faith, justification, conversion, regeneration, and so on. These are the spokes of the wheel, but they all center in Christ and radiate from Christ and reach the rim, which is God. They unite us in Christ with God.
To give all this its true and full value, it is necessary to contemplate or have revealed to us the meaning of Christ, to see what an immense thing has taken place by the Son of God becoming the Son of man, by God becoming incarnate. It is a question of our being taken, not into Godhead or Deity, but into God's Son incarnate.