In contrast to the East, the Western church (Rome and Protestantism) has had difficulty doing justice to the distinct identities of the three persons of the Trinity. Augustine compared them to memory, knowledge, and will — merely three aspects of a single mind — while Aquinas held that the three are “relations” in the one divine being. This trend has been pervasive — John Calvin and John Owen are notable exceptions — but, with the reappearance of the Eastern church on the radar, it is becoming recognized that equal justice should be done to the irreducible distinctions of the three persons.
This does not mean that we are to think of the Father, the Son, and the Holy Spirit on the basis of our understanding of human personhood, such as it is.
Once Trinitarian theology introduced the idea of “person” — it did not exist before — it inevitably came to have an independent history of its own. Consequently, we face a danger of importing modern concepts of personhood into our thinking on the Trinity.
We can be easily tempted to base our thoughts on human analogies, such as that of a human father and his son. This is what the Arians (fourth-century heretics) did; concluding that since a human son came into existence at a certain point in time, the Arians asserted that the Son of God began to be and so is not co-eternal with the Father but is of another being than He. Instead, since God is Spirit (John 4:21–24), we should think of Him in a spiritual manner; for instance, He is not a sexual being. The solution lies by way of the Incarnation. God as Father is the Father of our Lord Jesus Christ. But what exactly is the “Fatherhood of God” in this context? It is simply that He is the Father Jesus has. In short, we need to approach the matter from the other end. Personhood is to be understood in terms of the way God is three (insofar as understanding that is ever possible). He is an eternal communion of three persons in undivided union.
Peter Toon observes that “the Christian understanding of personhood flows from the Christian doctrine of the three persons who are God,” and so “if God is simply a monad then he cannot be or know personality. To be personal otherness must be present together with oneness, the one must be in relation to others” (Our Triune God, 1996, p. 241). C. S. Lewis agrees that God can only be love if He is triune: “All sorts of people are fond of repeating the Christian statement that ‘God is love.’ But they seem not to notice that the words ‘God is love’ have no real meaning unless God contains at least two persons. Love is something that one person has for another person. If God was a single person, then before the world was made, He was not love” (Mere Christianity, 1980 ed., p.174). And, we might add, if He were not love He could not be personal.
It is precisely on the question of love that the Islamic doctrine of Allah founders along with the Islamic doctrine of humanity. Only a God who is triune can be personal and, therefore, love. Human love cannot possibly reflect the nature of God unless God is a trinity of persons in union and communion. A solitary monad cannot love and, since it cannot love, neither can it be a person. And if God were not personal neither could we be — and if we were not persons we could not love.
In Philippians 2:5–11 Paul says, have this mind in you which was also in Christ Jesus. The incarnate Christ followed a path of obedience and humiliation, leading to the cruel and shameful death of the cross. He looked not to His own interests but to those of others. Moreover, His loving self-sacrificial obedience is the fruit of His decision not to exploit His status “in the form of God” for His own advantage, a decision made prior to His taking the form of a slave (vv. 6–7). This is what the eternal Son is like. We are to follow suit.
Hebrews 5 runs along similar lines, referring to Christ’s refusal to claim the office of high priest for Himself. Rather, He accepted His appointment from the Father, which was a self-effacing act that cannot be restricted to His incarnate ministry alone, since the appointment to high priesthood preceded the work of high priesthood itself.
Since, as Jesus said, he who sees Him has seen the Father, we can say further that this is not only what the Son is like from eternity but it is what God is like, too. Thus, the Father allows the Son to bring in the kingdom, the Son leads us to the Father, while the Spirit does not speak of Himself but testifies of the Son. This was pointed out originally by Gregory of Nyssa, when he wrote that in their mutual indwelling the three seek the glory of the others. There is, he says, “a revolving circle of glory from like to like. The Son is glorified by the Spirit; the Father is glorified by the Son; again the Son has his glory from the Father; and the Only-begotten thus becomes the glory of the Spirit” (On the Holy Spirit, Philip Schaff, ed. NPNF 5:324). The persons of the Trinity live in an indivisible union of love, seeking the glory of the other. When God seeks His glory, He is not pursuing self-interest like a celestial bully. It is not that He is more powerful than we and so His pursuit of His own glory wins out, come what may. His glory is the divine Trinitarian glory of self-giving love.
According to John, this intra-Trinitarian love is the basis for our love for God and other people. Since God Himself is love (1 John 4:16), and since we have fellowship and communion with Him, love is the acid test of our discipleship. If we love others, we belong to Jesus Christ. If we lack love, we are not His at all. The reason for this is that God is a triune communion of persons. Love is intrinsic to who He is. Attributes like grace, mercy, justice, and even holiness are all relative to creatures. His holiness is His separation from His creation. It is relative to the creature. In turn, His wrath is relative to sinners, as the expression of His holiness in response to human sin. Love, however, belongs to who He is in Himself in the undivided communion of the three persons. That is why He is called love in such absolute terms.
The Father loves the Son. The Son loves the Father. The Father loves the Holy Spirit. The Holy Spirit loves the Father. The Son loves the Holy Spirit. The Holy Spirit loves the Son. This reciprocal love of the three persons exists in the unbreakable union of the undivided Trinity. Insofar as we are enabled to be “partakers of the divine nature” (2 Peter 1:4), “from one degree of glory to another” by the Spirit of the Lord (2 Cor. 3:18), we are brought, in a creaturely way, into this communion of the love of God.