That, my friends, is an ontological statement—an ontological subordination—and it absolutely contradicts the Nicene formula. If (a) God is ontologically triune, (b) the triunity of God is defined by the relational distinctions of Father, Son, and Spirit, and (c) father-ness and son-ness necessarily implies authority and submission, then we must conclude that the supposed relation of subordination is necessarily definitive of the very being, nature, and essence of God. The subordination of the Son to the Father would be no more a functional role than is His eternity, omnipotence, or immutability.
[Much of this post first appeared as answer #2 of “Answering Four Common Laymen Responses to the ESS/EFS/ERAS Debate” published on the invaluable blog, A Daughter of the Reformation. I have republished a portion here since I continue to hear the claim that ESS proponents reject the ontological subordination of the Son to the Father in eternity; a claim that, unfortunately, cannot be maintained.]
Proponents of the Eternal Subordination of the Son (ESS) are indeed aware of and openly opposed to the Semi-Arian teaching of an ontological subordination of the Son to the Father, that is, a subordination and hierarchy within the very nature, essence, or being of God; for such a position clearly contradicts the Nicene Creed, dividing the one Nature and Will of God, calling into question the co-equality of the Persons. Rather, they locate this subordination and hierarchy of authority within relations of function or role amongst the persons of the Godhead. This, they claim, distinguishes their position from the Arian heresy and shields them from their critics. As Bruce Ware puts it,
[…]the Father’s authority over the Son does not indicate he is superior to the Son because 1) the Father and the Son each possesses the identically same nature and hence they are absolutely co-eternal and co-equal in nature, and 2) authority and submission describe merely the manner by which these persons relate to one another, not what is true of the nature of the Father or the Son. In other words, authority and submission are functional and hypostatic, not essential (i.e., of the divine essence) or ontological categories, and hence they cannot rightly be invoked as a basis of declaring one’s ontology (nature) greater and the other’s lesser. Ontologically, the Father and Son are fully equal, but as persons, they function in an eternal Father-Son relationship, in which the Father always acts in a way that befits who he is as Father, and Son always acts in a way that befits who he is as Son. Their Father-Son manner of relating (functioning) is seen (in part) in the authority of the Father and submission of the Son, as is evidenced by the vast array of the biblical self-revelation of the Trinitarian persons.
Or as Wayne Grudem states it,
The heresy of subordinationism, which holds that the Son is inferior in being to the Father, should be clearly distinguished from the orthodox doctrine that the Son is eternally subordinate to the Father in role or function[…].
But it seems clear to me (and others) that the words “function” and “role” are being used illicitly and beyond their normal meanings, in order to grant a veneer of plausibility to their unorthodox claims. To begin with, “function” already implies ontology, or properties of being, nature, or essence. Bruce Ware is absolutely correct when he states that, “function always and only follows essence. Put differently, what something can do is an expression of what it is”. That is part of the very definition of “function”! And the use of “role” fares no better when squared with the body of ESS/EFS/ERAS teaching, for a role is by definition not a necessary relation, nor an eternally fixed relation; a role could have been otherwise and can always become otherwise. If one is in an eternal, necessary, counterfactual-excluding relation, then one is simply not in a relation of role.
But in the end, regardless of the terms used, ESS is indeed about ontology and ontological subordination. “Ontology” is the study of fundamental being, nature, essence; it has to do with what makes something what it is, including what it must be to be what it is and what it cannot be and still be what it is. This is not the whole of the discipline of ontology, but it is essential to the meaning of “ontological”. When we speak ontologically of God, we are speaking of His very being, nature, and essence—those things which are fundamental to who He is and without which He is not who He is. Despite the reliance on “function” and “role” throughout the ESS literature, a simple ordering of the logic of their arguments quickly peels away the veneer of plausibility: