The doctrine of eternal generation is central to the doctrine of the Trinity; that the Son is begotten from the Father before the ages is the basis for several important parts of the doctrine of the Trinity, including the distinct personal existence of the Son, His Godhood, and His eternal sonship. That the Father begat the Son before the ages is the very reason why the Father is eternally Father, and the Son eternally Son, and is the basis for the relationship They have with one another. It is without a doubt then, one of the most crucial doctrines in Christian theology.
That the Father begat the Son, is of course, an analogy of language. When we speak of ‘begetting’ in creatures, we refer to something bodily and carnal, in the procreation of progeny by a father. When scripture uses this language to communicate divine truths about God and His Son to us, we are of course to understand this analogy then as being exactly that; an analogy. To take it in too literal a sense, and to draw too literal of a parallel between the idea in relation to creation and the divine generation of the Son, will inevitably result in error in this important doctrine. And in light of how central this doctrine is to a biblical understanding of the Trinity and Christian theology, errors in this doctrine tend to have major ramifications.
One of the central aspects of one of the most famous doctrinal errors in history hinged upon a misunderstanding of this concept. Arius, in articulating the Son’s eternal generation from the Father, wrongly applied the analogy too literally; he took that which is true in the case of creatures, and applied it back onto God illegitimately, in a way that scripture does not intend us to. Arius reasoned, that since in the case of human generation, a son does not exist prior to his generation by his father, that the Son of God, therefore, did not always exist, because He was generated, and therefore, like a human son, must have not existed prior to His generation from the Father.
Arius’s logic in respect to humanity holds up; although perhaps a son may be said to exist in potentiality prior to his generation, a human son does not personally exist until he is begotten by his father, at which point he takes on a distinct personal existence. A human son, in the process of being generated, goes from nonexistence to existence, and so, as Arius correctly reasoned, does not exist prior to being begotten.
But Arius erred in his reasoning, by thinking that the same would be true in respect to God and His Son; He ignored God’s uniqueness, and the way in which God is different than man, in how he thought through this analogy’s application to the Son’s divine generation. God, after all, is eternal, and unchanging. This means that as He is Father, He has always been Father, eternally, and unchangingly. There is no point in time at which God went from not being Father, to being Father; He is so eternally and unchangingly. This is totally different than man, who goes from not being a father to being a father at some point in time, and who is always changing throughout his life.
Additionally, God’s generation of His Son took place before and outside of time (since time, being part of creation which was made through the Son, did not yet exist, so to speak). Since man was created in time, and only knows a temporal existence, this is a difficult concept for us to grasp. Since we are temporal creatures, all human generation takes place in time; but the Father begat the Son outside of time, and so, the situation, in that respect, is not analogous to our human experience. Thus conclusions drawn about the Son’s generation on the basis of a parallel in this respect are doomed to be flawed.
Arius erred greatly, then, when he proclaimed that just as a human son does not exist prior to his generation, so the Son of God did not exist prior to His generation, and there was a time when He was not, and that the Father was without the Son. The ultimate basis for this error was that Arius, in learning from the analogy of generation that God has given us in the scriptures to reveal His relationship with the Son, did not take into account God’s uniqueness, and the ways that God and man differ. Had he better taken into account the differences between God and man, that God does not change, and that His begetting of His Son was atemporal and outside of time rather than within it, he would not have made such errors. There can never have been a time when the Son was not, for the Son was begotten before time was created; and the Son has always been with the Father, and the Father is eternally and unchangingly Father.
Despite the vast difference between Arian and Athanasian theology, the Athanasian view of eternal generation errs in fundamentally the same way; it takes the analogy of human generation and applies it to God and His Son in an illegitimate way, because, as Arius’s doctrine did, it ignores God’s uniqueness, and the differences between God and man. It takes that which is true of man and not of God, and applies it back onto God, thereby using a good analogy that God gave us in the scriptures to reveal His relationship with His Son, to ultimately misrepresent that relationship.
What I mean is this: the Athanasian view of eternal generation reasons from the true fact that human father and son are defined by the same, identical set of ontological attributes, that therefore, God and His Son must also have the same exact set of ontological attributes. Every created son inherits a set of natural ontological properties from his father which he shares with his father; and so, it is reasoned, the Son of God inherits the ontological properties of His Father. Just as man, as a rational, mortal animal, begets from himself another individual who is equally a rational, mortal animal, so it is reasoned that the invisible, infinite God begat from Himself an equally invisible, infinite Son.
Yet this parallel, like that which Arius drew, flounders on the fact of God’s utter uniqueness, and the differences between God and man, which this view fails to take into account. For man to have an ontological equal is expected; we were created in such a way, and with such a nature, that we pass down to our descendants an identical set of ontological properties. This is true broadly in creation, and so everything reproduces after its own kind. Yet God is utterly unique; He tells us plainly that He has no ontological equal: “To whom would you liken Me, And make Me equal and compare Me, That we would be alike?” (Isaiah 46:5 NASB). And the Son likewise testified that “the Father is greater than I.” (John 14:28 NASB). God is ontologically unique, as, for instance, He alone of all things has no cause, source, or origin. All other things are caused by the Father; the Son is eternally begotten from the Father; the Spirit eternally proceeds from Him; and all creation was made by Him through the Son; yet He alone of all things simply is, eternally and unchangingly, without any cause, source or origin. And so God, in being unoriginate, is utterly unique. And having a unique existence, He has certain attributes that are simply impossible for other beings to share.
Among these is His infinitude. God, the Father, alone, of all things, is absolutely infinite, being beyond all bound, all limitation, and all measurement. Having no origin and no superior, He simply eternally and unchangingly is and exists, and there are no external limits upon Him whatsoever; but He, as the cause and source of all, sets the limits and bounds of all other things. And all other things, no matter how transcendent and great they may be, in having an origin of some sort or another, are in that sense as well, bound and limited. And it is impossible, according to the very nature of things, that there could be two infinite persons or beings; for if one were greater than the other, the greater would be a limit to the lesser, and so, only the greater would be infinite; and if two were conceived of as equal, each would pose a limit to the other, and constitute a measure of the other, and so, neither would be infinite. The Father then, being infinite, is alone infinite; and this ontological attribute is not communicable to another.
The mistake of Athanasian theology, then, is to suppose that all of God’s ontological attributes, like those of men, are such that can be communicated to another individual by generation, so as to result in another distinct person who is ontologically equal to the first. God’s attributes are far different than man’s; and while all of man’s natural ontological attributes are such that can be communicated to his offspring by generation, God, being unique, possesses attributes which according to the very nature of things are impossible to communicate to another. The Son is certainly like the Father, and bears the image of His Father (as in the case of a human father and son also); yet the Son does not for this reason possess all the same ontological attributes as His Father. While He transcends all creation, for example, as the one through Whom all creation was made and is upheld in its existence, He is not, like His Father, absolutely infinite. While the Son is light from light, no one will say that a finite light is ontologically identical to an infinite light; although the former is the perfect image of, and the exact representation of the latter, both being truly light. So the Son, begotten of the Father before the ages, is like His Father, and is the Image of His Father; yet not in such a way that we should imagine that He shares in all the unique ontological traits of the Father.
The mistake, then, of Athanasian and Arian christology is the same: both apply what is true in the case of human generation to God, although it is not applicable, because of the differences between God and man. By failing to account for these differences, both make the mistake of attributing things that are true in the case of creatures, but not of God and His Son, to God and His Son. Arian christology neglects that God’s generation of His Son took place outside of time, and that the Father is unchanging, and so, eternally Father. Athanasian christology neglects that God is utterly unique, and that as such, not all of His ontological attributes are communicable. Arianism denies that the Father is eternally Father, and that the Son is eternal in His existence, and Athanasian christology denies the Father’s ontological uniqueness, and creates a logical quandary that leads men to modalism; for in proclaiming that the Son is equally infinite with the Father, it leads men to think that the Son is the same person as the Father, since it is impossible that there be more infinite persons than one, and so, in order to make the Son infinite, He is also made to be the same person as the Father Himself.