(note: this post comes closely on the tail end of a three part discussion of the incarnation of Christ; click here, here and here to read these posts)
One manner in which it can be beneficial to understand the truth and content of a particular state, or proposition, or event, or action, etc., is to consider the consequences of the same had it been another way. That is, we can (potentially) learn about reality by contemplating possible alternatives to that reality, whether they are or were indeed possible/actualizable or not. With that in mind, What would be the consequence of the following statement, if indeed it were true?
a. Jesus Christ was/is willing to offer Himself for the life of the world (but, He did not or has not yet done so)
Would this mere willingness-without-demonstration depreciate or augment the Christian gospel? Hopefully, it does not take any convincing to recognize that the former of these consequences would result, and not the latter. Narrowing closer on the present topic, that of the goal of the incarnation of Jesus, consider a second, but similar proposal, What would be the consequence of the following statement, if indeed it were true?
b. Jesus Christ was/is willing to become human for the sake of humanity and for the glory of God (but, He did not or has not yet done so)
The reason I here invoke these possible "alternative" circumstances (that are, of course, totally fabricated) relating to Christ's incarnation is so that we might understand more fully (to the extent that we are able) not just the reality, but also the necessity of Jesus becoming incarnate: "He had to be made like His brethren in all things, so that He might become a merciful and faithful high priest in things pertaining to God, to make propitiation for the sins of the people" (Hebrews 2:17, emphasis added). The claim of Christianity is not just that it is a historical fact that a man named Jesus, who is called the Christ, lived on this earth and died for the sins of the world. It is much stronger than that. Christianity asserts, in conjunction with historical reality, that it was necessary for Jesus, who is the Christ, to become human, live a perfect and sinless life, suffer and die for the sins of the world, rise again on the third day to conquer death through death and ascend into heaven to be seated "at the right hand of the Majesty on high" (1:3). In a sense that we will explore below, Jesus was obligated to "partake" of the very "flesh and blood" that "the children [His brethren] share" (2:14).
But now we have introduced a notion that demands clarification, for, how can Jesus, being Himself God, be obligated towards anything? This can be answered in (at least) two ways. One response is to say that it is (although at first it may seem contrary to what I have just claimed) wholly correct to maintain that the Triune God, and all Persons of the Triune God, are not obligated to do anything. Obligations often come from something external to the self, and God is the only eternal Person who is entirely self-existent and, therefore, in no position to be obligated by His creation. For example, He created the universe and all that is out of complete freedom and love, and not out of any need or obligation. The only way in which God may be said to be properly obligated toward anything (though this statement needs careful consideration and perhaps refining) is that He is (self-)constrained by His own eternal nature. For example, we know from God's self-revelation to humankind that, among many other things, God is love, God is merciful, God is just, God is eternal, God is immutable, and God is holy. Perhaps, then, we may say that God is obligated to be love, to be merciful, to be just, immutable and holy. God is obligated in that He, in a sense, constrains Himself - He cannot be, for example, unholy.
This brings us to the second response to which it may be possible for any or all Persons of the Trinity to be obligated towards something. That is, given the exigencies of a particular situation, something could not be another way (and this, in turn, could relate to principles of God's creation that God instilled or embedded into it). So, for example, given that God created (among everything else) humanity, and that humanity not only disobeyed God, but also "ceased to be hungry for Him and for Him alone," perhaps it is necessary from these circumstances that God should enter into humanity in order to redeem us (Schmemman 1973:18). Thus, as the author of the epistle to the Hebrews writes, "[Jesus] had to be made like His brethren in all things" - it was absolutely necessary for Jesus to become incarnate. Still, now we are confronted with yet another dilemma, and we may ask, Why was it necessary? This is the point to which the author brings us, and this can be understood by reference to the aforementioned hypothetical situation, wherein Jesus possessed willingness to become human, but did not actually do so.
This question of "Why was it necessary?" in light of the possibility of mere willingness-without-demonstration takes us back to the beginning of creation, wherein the eternal, loving, omniscient, merciful, and holy Triune God created all things and then blessed them as being "good" (Genesis 1:1-31). Among the creation, humanity was also blessed with a unique position among the created realm, so that we who have been made in the image of God might enjoy His creation, returning it to Him in thanksgiving, communing with Him and enjoying Him forever (for which purpose we were created). Yet, although sin was not initially introduced into creation by humanity, Adam and Eve failed to see God as their all-sufficiency and thus disobeyed Him, transgressing against His loving words (which were for their good) and rupturing the intimacy and communion for which they had been created. As a result of this action, "sin entered the world, and death through sin" (Romans 5:12). Moreover, even until now, we actively participate in such rebellion universally (3:23).
Our sin, therefore, puts us in quite a singularly devastating predicament, whose effect is twofold. We cause(d) the separation that exists between ourselves and God, and, therefore, we (humanity) have the responsibility and (even individual) accountability to reconcile the rift we have created. Yet, paradoxically, we are not able, in and of ourselves, to draw near and reconcile ourselves to a holy God. Thus, our circumstance demands reparation and restoration that is initiated by us, but, simultaneously, we are now universally and individually in no position to effectualize the perfection in us that we so desperately need in order to fulfill the requirement that enables us to again commune with the divine. Communion, again, relates to the purpose of humanity in relation to the purposes of the divine will, and this intimacy with Him is what provides us with utter satisfaction and enjoyment, for we participate in a direct and meaningful relationship with the One who is above and before all things. Still, we are presently confronted with our complete helplessness.
How does God remedy this broken relationship? One possibility is that He perhaps grants automatic cleansing of sin and therefore there is no need for the incarnation. However, let us not even go so far as to say there is no need, for we can reject this proposition by treating a similar one, namely, that God (i.e., Jesus) was willing (but did not actually) become flesh and blood; instead, God enacts reconciliation without such drastic means and just offers reconciliation in a (seemingly) straightforward manner. At this point we might ask the question, Does this really remedy the problem? According to Hebrews 2:17, according to Christianity - and if these truly have their origin in God Himself then we may also be bold enough to declare, and according to God - this neither does nor could produce the salvation of which we (i.e., all of humanity) are in need.
According to Hebrews 2:17, the reason for this relates to the role of Christ as the "merciful and faithful high priest [...] to make propitiation for the sins of the people." Though we will return to the concept of high priest when we discuss various points in Hebrews 5-10, a basic "definition" that will be important to bear in mind is that "every high priest taken from among men is appointed on behalf of men in things pertaining to God, in order to offer both gifts and sacrifices for sins" (5:1). Also important to the present verse and its mentioning of certain purposes of the incarnation is that Jesus "make[s] propitiation for sins" (2:17). And, though it seems quite obvious to state this, if there is an act of propitiation then there must first exist a need for that propitiation such that the particular act in question can alone offer satisfaction. This need was instantiated by the fall of Adam and Eve, which spread to all of humanity, and so brought death to all humanity. Sin causes separation between us and an all-holy God, and as He is holy and just we incur a just wrath that obligates satisfaction and appeasement for, being holy, God cannot ignore or overlook sin.
But this becomes the beautiful truth of the Christian gospel: God does not ignore sin. Even though we caused ourselves to be left in an utterly helpless estate, God is not so powerless nor is He without mercy and love that He allows us to remain without the highest good that we can possess: Himself. God, even though He is holy and pure (and, thus, not only sinless but not capable of sin) actually and directly initiates reconciliation on our behalf through Jesus Christ. As we consider the verse in Hebrews 2:17, and the truth of the incarnation and Christ's propitiatory sacrifice, we must contextualize these verses in the prior argumentation (especially chapter 1) wherein the writer definitively and unambiguously maintains the deity of Christ. Therefore, by God Himself condescending and taking our flesh and blood upon Himself, He effectively overcomes the seemingly impossible barrier that we have erected: God remains all-powerful, merciful, sovereign, holy, loving, and all-sufficient, yet by entering into humanity and offering Himself as a pure sacrifice He is able to fulfill the demand placed upon us as the result of our sin. The work that Christ came to do, the salvation that He Himself inaugurated, demanded a genuine incarnation wherein God dwelt among us in human flesh in order to, as we read later in Hebrews 9-10, offer up Himself as a perfect sacrifice for the life of the world. As a result, it is in no way arbitrary, nor is it for mere expediency that Christianity upholds the glorious truth of the incarnation which is (in part) treated in Hebrews 2:17. Rather, Jesus was, in this sense, obligated to become God incarnate: "He had to be made like His brethren in all things." Moreover, it is not truly possible that Christ merely desired or was willing to become incarnate without genuine action. For this reason:
God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Much more then, having now been justified by His blood, we shall be saved from the wrath of God through Him. For if while we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life. And not only this, but we also exult in God through the Lord Jesus Christ, through whom we have now received the reconciliation. (Romans 5:8-11)
So we may say that it was absolutely necessary for Christ to become human, to offer Himself as a perfect sacrifice by blood that was His own, and to rise again so that He would, by way of humanity, conquer death that spreads to us all as a result of sin. In his death, the death which He verily died as a human, He reconciles us to God, overcoming the separation between us. And furthermore, in His resurrection, He invites us to experience communion with God in newness of life - life in Him and through Him.
At times it amazes me how wont people have been throughout history to deny the essential truths of the incarnation. Such activity usually focuses narrowly on only one aspect of the twofold truth expressed in the hypostatic union (the union of two natures in one Person, Jesus Christ). For example, some admit to the human Person of Christ, but deny any possibility that the divine could, say, co-mingle with fallen and sinful humanity. This may at times be in a supposed effort to preserve the holiness of God in His work of salvation, but it effectually renders Him passively operative by only having some degree of indirect involvement in salvific work. On the other hand, some admit to the deity of Christ but reject His having dwelt among us in physical, bodily form. This, too, may be in an effort to preserve some aspect of Christ's Person, namely His deity, but it fails in that it falsely conceptualizes God's relation to the physical world and the purposes He has for it through Jesus Christ. A biblical doctrine of the incarnation necessarily admits to the reality of the hypostatic union in spite of its mystery (or it may be better stated, because of its mystery), for it proclaims that someone other-than-human became clothed in human flesh. This Other Person was and could be no less than God Himself who became incarnate in holy condescension, so that it might be truly said that with God - who is holy, loving, just, merciful, and righteous - all things are indeed possible.
Schmemman, Alexander. (1973). For the Life of the World: Sacraments and Orthodoxy. Crestwood, NY: St. Vladimir's Seminary Press. (Original work published 1963)