Herman Bavinck, Reformed Dogmatics, III:214-15:
This doctrine of the pact of salvation… is rooted in a scriptural idea. For as Mediator, the Son is subordinate to the Father, calls him God…, is his servant… who has been assigned a task… and who receives a reward… for the obedience accomplished… Still, this relation between Father and Son, though most clearly manifest during Christ’s sojourn on earth, was not first initiated at the time of the incarnation, for the incarnation itself is already included in the execution of the work assigned to this the Son, but occurs in eternity and therefore also existed already during the time of the Old Testament… Scripture also clearly… sees Christ functioning officially already in the days of the Old Testament… The pact of salvation makes known to us the relationships and life of the three persons in the Divine Being as a covenantal life, a life of consummate self-consciousness and freedom… Among the three persons, it is a pact (suntheke) in the full sense of the word. The greatest freedom and the most perfect agreement coincide. The work of salvation is an undertaking of three persons in which all cooperate and each performs a special task. In the decrees, also in those of predestination, the one will of God occupied the foreground, and their trinitarian character was still blurred. But here, in the pact of salvation, the work of redemption stands out in its full divine splendor. It is the divine work par excellence. Just as at the time of the creation of humanity, God intentionally consults with himself in advance (Gen. 1:26), so, in the work of re-creation, each of the three persons even more clearly acts in his own distinct character. The of re-creation, like that of creation, is a work of God alone: of, through, and unto him are all things… It is the triune God alone, Father, Son, and Spirit, who together conceive, determine, carry out, and complete the entire work of salvation.
This pact of salvation, however, further forms the link between the eternal work of God toward salvation and what he does to that end in time. The covenant of grace revealed in time does not hang in the air but rests on an eternal, unchanging foundation… It is a false perception that God first made his covenant with Adam and Noah, with Abraham and Israel, and only finally with Christ; the covenant of grace was ready-made from all eternity in the pact of salvation of the three persons and was realized by Christ from the moment the fall occurred.
The underline and bold in the first paragraph are mine. I highlight these to illustrate a point I made in my previous post about the trinity debate. The language of EFS does not designate one view. It describes a family of views that share in common the idea that the preincarnate Son submits to the Father in some qualified sense from all eternity. It doesn’t specify any particular trinitarian implication. You have to examine the individual writer’s view in order to discover that information.
In Bavinck’s case, EFS is explicitly connected to the covenant of redemption. The Son’s relation is described as “subordinate” and issues forth in “obedience” and that relationship “was not first initiated at the time of the incarnation” but “occurs in eternity.” But it must be stipulated that Bavinck is speaking analogically, not univocally about “subordination.” He clearly qualifies this term by his larger trinitarian views which include a commitment to the entire Nicene package (e.g., eternal generation, single will of God, inseparable operations, etc.). In other words, the “subordination” is a feature of the trinitarian economy, but that economy commences in the eternal covenant of redemption.