Having considered the divine persons individually, we must now turn to their mutual inherence in one another in virtue of their one divine essence— what is commonly called in theology perichoresis.
Perichoresis is a Greek word that was first employed by Gregory of Nazianzus in the fourth century to refer to the mutual inherence of the divinity and humanity in Christ.
However, with time, this term—along with its Latin rendering, circumincessio—came to be used in theology to refer primarily to the mutual inherence or indwelling of the three persons of the Holy Trinity in one another.
The key idea: Not only do the persons proceed from one another; and not only does each of the persons have in himself all that pertains to the divine essence or being; in addition, each person is simultaneously within the others, and in a reciprocity of communion with the others, without ceasing to truly be himself.
How can this be?
Aquinas identifies 3 foundations for speaking about perichoresis (ST I, q. 42, a. 5):
1: Unity of Essence
When speaking of the equality of the three persons in God, Aquinas begins with a “Nicene starting point” by maintaining that the absolute equality of the persons is ultimately derived from the fact that they are mysteriously homoousios, one in being and essence. It is principally on account of the “unity of essence” that “the persons are equal to one another.
2: Reciprocity in relations
Whereas human or creaturely spiritual relationality develops always from the outside, or exists through a distinction of beings, in God, the relation of persons is wholly immanent, so that all that one person is is transparent to the other because it is relationally given or received from the other. Thus, there is a perfect communion of persons in God made possible by the greatest immanent relational reciprocity (as each person is immanently present to the others personally in all that they are, as principles of personal giving or receiving).
3: Origin
The processions are not only from the Father, but also within the Father, as the Father’s generated Word and spiration of Love remain eternally within their principle of origin. Therefore, in proceeding from the Father, the Son and the Spirit do not “leave” the Father. Rather, even as they are constituted as distinct from the Father by way of the processions and in relations of origin, they are ever likewise “toward” the Father and indwell him in the one divine essence, as he too abides in them.
Implications for the work of God ad extra in the economy:
- BOTH: It is always the work of all three persons together. “The economy is the theatre in which the mystery of the eternal life of perfect personal communion in God is manifested truly to the human race and in which human beings are invited into personal communion with the Holy Trinity” (510). The action of each one implicates the other two (in virtue of their shared divine nature). In the economy, this means that when one person is sent on mission from another, so as to act in the world, the other two are wholly present and active in that person.
- AND: Each person acts in a distinctive mode. The Father’s paternal mode. The Son’s filial mode. The Spirit’s spirated mode. Each acts in a wholly personal way in the unique personal mode proper to each.
“The perichoresis or mutual indwelling of the persons, then, refers to the way the three co-equal, co-eternal persons continuously abide within one another, but each according to the mode or manner in which they possess the divine nature, which in turn is based upon their respective relations of origin” (519).
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