All that to say, if the Son’s generation is eternal, so also it must be immutable. Where there is a succession of moments (time), change will follow; indeed, it must. But in eternity, there is no successiveness and therefore no mutation in God. The Father begets His Son not as a new moment in time but from eternity. To say, as the Nicene fathers did over against the Arians, that there never was a time when the Son was not is to also confess there never was a time when the Son was not immutable. If He was not begotten out of the eternal, immutable nature of the Father, then we would be right to ask whether something is lacking in God, whether God Himself is incomplete and imperfect.
In our last adventure, we were warned against nine marks of an unhealthy generation. If you are just joining us, we are talking not about human generation but about the eternal generation of the Son from the Father. From all eternity, the Father communicates the one, simple, undivided divine essence to the Son. We discovered that this eternal generation cannot involve any multiplication or division of the divine essence.
What else must be excluded from this divine generation? Don’t take that question lightly. As I explain in Simply Trinity: The Unmanipulated Father, Son, and Spirit, a right answer might just guard you from heresy, especially considering the dangers that lie at the end of our adventure. Consider with me two final marks of an unhealthy generation.
No Priority, No Posteriority, No Inferiority
The Son’s generation involves no priority or posteriority, and certainly no inferiority but designates order alone. If it did involve priority or posteriority of any kind, then the Son would be inferior to the Father.
Previously, I emphasized that the Son is begotten by the Father, but unlike our human experience, the Son’s generation is eternal (before all ages, timeless). And if eternal, then the generation of the Son is not the generation of a lesser being (made in time or before time) but the generation of a Son who is equal in deity to His Father. But the reason the Son is not inferior to the Father is because the one divine essence wholly subsists in the Son due to His generation from the Father’s nature or substance. As the Son is true God from true God, there can be “no diminution of the Begetter’s substance” in the generation of the Son.1 The Father begets His Son, and the two are, to return to that key word from Nicaea, consubstantial, meaning they are to be identified by the self-same divine essence. Priority or posteriority would undermine the Son as consubstantial, as One who is of the same nature as the Father.
As we’ve learned, the lack of priority or posteriority is due in part to the timeless nature of the Son’s generation, which is eternal, not temporal. Gregory of Nazianzus was once asked why the Son and the Spirit are not co-unoriginate along with the Father if it is true that they are coeternal with the Father. His response: “Because they [Son and Spirit] are from him [Father], though not after him. ‘Being unoriginate’ necessarily implies ‘being eternal,’ but ‘being eternal’ does not entail ‘being unoriginated,’ so long as the Father is referred to as origin.” To drive this point home, Gregory appealed to the illustration of the sun. “So because they [Son and Spirit] have a cause they are not unoriginated. But clearly a cause is not necessarily prior to its effect—the Sun is not prior to its light. Because time is not involved, they are to that extent unoriginated—even if you do scare simple souls with the bogey-word; for the sources of time are not subject to time.”2
With a nudge from Gregory, consider the biblical imagery of light (John 1:4, 8–9). The Nicene Creed says the Son’s eternal generation from the Father can be compared to “light from light.” The Cappadocian Fathers (Basil the Great, Gregory of Nyssa, and Gregory of Nazianzus—key fourth-century church fathers who helped clarify our doctrine of the Trinity) also appealed to this imagery of light to counter the belief of subordinationists who said an effect is inferior to its cause, the Son subordinate to the Father. Consider the sun, they said in response. It is the cause of light, but by no means is light inferior to its source. In essence, they are one and the same. How much more so with divinity? Is not the divine essence simple and inseparable, eternal, and immutable?
We might also add that the Son cannot be less than His source (the Father), because there is no hierarchy in the Trinity. The Father is not greater than the Son—not in any way. In order to avoid misunderstanding, some may prefer the word source instead of cause (as I do) when talking about the Father, which better safeguards the Son’s equality. But regardless, in the Great Tradition neither word means the Son has a beginning or is less than the Father because He is from the Father.
In sum, the Father is the principle in the Godhead—the principle who alone is without principle. Unbegotten. But that does not mean that the Father and Son are not coequals. Rather, the eternal relations reveal the origins of the persons. To read hierarchy of any kind into these origins is to abuse them, even manipulate them. (This includes recent attempts to subordinate the Son to the Father within the immanent life of the Trinity.) The Father may be the principle without principle, but He is also the “principle without priority.”3 Whenever we or the Great Tradition uses words such as source, the intention is only to identify the personal origin of the Son: the Father. Hierarchy and priority are precluded by the very nature, will, power, and glory the three persons hold in common. As Gregory of Nazianzus says: “They do not have degrees of being God or degrees of priority over against one another. They are not sundered in will or divided in power. You cannot find there any of the properties inherent in things divisible.” In short, “The Godhead exists undivided.”4