“It is customary to say that he (the author of Hebrews) insists upon the possession by Christ of our human nature as essential to His priestly representation of us. But this is not saying enough. The line of reasoning followed in the second chapter shows plainly that the solidarity lies back of this, that the assumption of human nature through the incarnation is not its basis but only a form in which the principle asserts itself. When we are told that ‘both he that sanctifies and they that are being sanctified are all of one’ (2:11), it would be a mistake to interpret this phrase ‘of one’ of the common descent of Christ with us from Adam or Abraham. That something else is meant the working out of the idea in the sequel convincingly shows. For the author proceeds to prove this fact of this solidarity from the observations that Christ calls believers His spiritual brethren, and that He resembles them by assuming the same trustful attitude towards God which marks them as children of God, nay that He Himself sustains to them the relation of a father to his children. All this lies in the spiritual sphere and while, in its concrete form, not possible w/o the incarnation, is not in principle caused by it. On the contrary, the author represents the incarnation as the further carrying out of a spiritual solidarity already given: “Since then the children are sharers in flesh and blood, He also Himself, in like manner partook of the same.” (Heb. 2:14). The joint-sonship of Christ w/ believers does not follow from the incarnation, it produces the incarnation: because those w/ whom He was spiritually identified, those whom He resembled in sonship, partook of flesh and blood, He carried His solidarity w/ them to the point of the assumption of their nature. It is obvious that the root of the identification of Christ w/ us which underlies His priesthood is in His standing before God, in the divine appointment by which His destiny and the destiny of the people of God were forever united. It is what the old theology called the federal oneness of Christ w/ believers that is here taught. That this idea is actually in the writer’s mind follows from one striking feature in the representation which is often overlooked. Believers are not merely called joint-children of God with Christ, but are called ‘children of Christ.’ The writer puts on the lips of Jesus the Isaianic utterance: ‘Behold I and the children whom God has given me’ (2:13) and joins to this the affirmation that, because the children, i.e., Christ’s children, were partakers of flesh and blood, He also Himself in like manner partook of the same. They were His children because back of all temporal developments in either His birth or their Birth, they had been given to Him of the Father. He stands not only in general solidarity with them, but in that specific form of solidarity which constitutes Him the Father and them the children – a representation which is unique in the New Testament, where believers are elsewhere called the children of God and the not the children of Christ.

Geerhardus Vos
Redemptive History & Biblical Interpretation –pg. 209-210

A significant problem in much of the Church’s thinking today is its inability to see the temporal as being conditioned upon the eternal. One example of this is discussions regarding union w/ Christ. Currently there is a debate in the Reformed Church as to whether or not union w/ Christ yields forensic justification or whether forensic justification is logically prior to union w/ Christ. My contention, is that both schools have a problem because neither school seems to want to make distinction between existential subjective union w/ Christ, Historic objective union w/ Christ and eternal objective union w/ Christ. Nor does either school currently debating seem to want to make the distinction between existential subjective justification, Historic objective justification and eternal objective justification.

We have to realize that the point that Vos makes here is that before we can talk about a existential subjective union w/ Christ that occurs when the Spirit of Christ applies the benefits of salvation to me personally we must talk about the historic objective union that was in place between the believe and Christ even in Christ’s incarnation and then in His baptism, death, resurrection and ascension. The subjective existential union w/ Christ that was applied by the Spirit to the elect was applied because the elect were united to Christ objectively in all the redemptive work that He accomplished. But even this union w/ Christ has need to be traced back one step further to realize that both the objective Historic union w/ Christ that the elect had when Christ came and the existential union that came into existence when the Spirit made that historic objective union subjective in his application of salvation upon individually elect believers is itself predicated upon the reality that the elect have objectively, from eternity always been united to Christ. This is the point that Vos is making above. The debate isn’t whether or not Subjective existential union w/ Christ is logically antecedent or subsequent to subjective forensic justification. The debate is whether our eternal union w/ Christ is logically antecedent or subsequent to our eternal justification in Christ. All that becomes subjectively true of us when we look to and trust Christ is only true because it was all objectively true in Christ’s death and all that was objectively true in Christ’s death was objectively true from eternity past in the counsels of God.

There has never been a time when the elect have not been united w/ Christ, (this is Vos’ idea of solidarity above) though for many it was true that that the eternal and historic objective truth was not yet a subjective reality. Notice how all this flows seamlessly. What is objectively true in eternity becomes objectively true in space and time by virtue of Christ’s finished redemptive work and this then becomes true existentially for the believing one as the Spirit perichoretically administers the union Planned from eternity by the perichoretic work of the Father and executed in time by the perichoretic work of the Son.

There is much much more to be said here and I may return to this later. We need to speak of how we end up with a works salvation if we don’t make the kind of distinctions we are speaking of here. We need to speak further about the relation between eternal justification and eternal objective union w/ Christ. We need to speak further about the relation, role and character of faith both with these distinctions and without these distinctions.

For now, let what Vos has said sink in. Vos appeals to Hebrews 2:10f to remind us that there has always been from eternity a solidarity (objective eternal union) between Christ and His people. This is significant exegesis and theology because when properly understood this insight moves one from Reformed to Reformed.