Philip Graham Ryken in Justification and Union with Christ:
Union with Christ is not simply one step in salvation; it is the whole stairway on which every step is taken. Or perhaps it would be better to say that union with Christ is the prism through which all the other colors of salvation are refracted. Our election is in union with Christ, for it is in Christ that we were chosen before the creation of the world (Eph. 1:4). Our regeneration is also in union with Christ, for the Scripture says we are created in Christ; and this re-creation is for good works, which means that our sanctification is in union with Christ as well (Eph. 2:10). In short, everything up to and including the doctrine of glorification is in union with Christ, for those who share in his sufferings will also share in his glory (Rom. 8:17).