Some thirty years ago, Karl Rahner claimed that most Christians are “mere monotheists,” that if the doctrine of the Trinity proved to be false, the bulk of popular Christian literature, and the mindset it reflects, would not have to be changed. Unfortunately, this is largely still true.
Defining the doctrine of the Trinity as a mystery that cannot be fathomed by unaided human reason invites a position such as Melanchthon’s: “We adore the mysteries of the Godhead. That is better than to investigate them.” But the danger of not reflecting carefully on what has been revealed, as it has been revealed, is that we remain blinded by our own false gods and idols, however theologically constructed.
So how can Christians believe in and worship the Father, the Son and the Holy Spirit, and yet claim that there is only one God, not three? How can one reconcile monotheism with Trinitarian faith?
My comments here follow the structure of revelation as presented in Scripture and reflected upon by the Greek Fathers of the fourth century, the age of Trinitarian debates. To avoid the confusion into which explanations often fall, it is necessary to distinguish between: the one God; the one substance common to Father, Son and Holy Spirit; and the one-ness or unity of these Three.
The Father alone is the one true God. This keeps to the structure of the New Testament language about God, where with only a few exceptions, the world “God” (theos) with an article (and so being used, in Greek, as a proper noun) is only applied to the one whom Jesus calls Father, the God spoken of in the scriptures. This same fact is preserved in all ancient creeds, which begin: “I believe in one God, the Father…”
For us there is one God, the Father… and one Lord Jesus Christ (1 Corinthians 8:6). The proclamation of the divinity of Jesus Christ is made no so much by describing Him as “God” (theos used, in Greek, without an article is as a predicate, and so can be used of creatures; cf. John 10:34-35), but by recognizing Him as “Lord” (Kyrios). Beside being a common title (“sir”), this word had come to be used, in speech, for the unpronounceable, divine, name of God Himself, YHWH. When Paul states that God bestowed upon the crucified and risen Christ the name above ever name (Philippians 2:9), this is an affirmation that this one is all that YHWH Himself is, without being YHWH. This is again affirmed in the creeds. “And in one Lord Jesus Christ, the Son of God… true God of true God.”
According to the Nicene Creed, the Son is “consubstantial with the Father.” St. Athanasius, the Father who did more than anyone else to forge Nicene orthodoxy, indicated that “what is said of the Father is said in Scripture of the Son also, all but His being called Father” (On the Synods, 49). It is important to note how respectful such theology is of the total otherness of God in comparison with creation: such doctrines are regulative of our theological language, not a reduction of God to a being alongside other beings. It is also important to note the essential asymmetry of the relation between the Father and the Son: the Son derives from the Father; He is, as the Nicene Creed put it, “of the essence of the Father” – they do not both derive from one common source. This is what is usually referred to as the Monarchy of the Father.
St. Athanasius also began to apply the same argument used for defending the divinity of the Son, to a defense of the divinity of the Holy Spirit: just as the Son Himself must be fully divine if He is to save us, for only God can save, so also must Holy Spirit be divine if He is to give life to those who lie in death. Again there is an asymmetry, one which also goes back to Scripture: we receive the Spirit of Him who raised Jesus from the dead as the Spirit of Christ, one which enables us to call on God as “Abba.” Though we receive the Spirit through Christ, the Spirit proceeds only from the Father, yet this already implies the existence of the Son, and therefore that the Spirit proceeds from the Father already in relation to the Son (see especially St. Gregory of Nyssa, To Ablabius: That there are not Three Gods).
So there is one God and Father, one Lord Jesus Christ, and one Holy Spirit, three “persons” (hypostases) who are the same or one in essence (ousia); three persons equally God, possessing the same natural properties, yet really God, possessing the same natural properties, yet really distinct, known by their personal characteristics. Besides being one in essence, these three persons also exist in total one-ness or unity.
There are three characteristics ways in which this unity is described by the Greek Fathers. The first is in terms of communion: “The unity [of the three] lies in the communion of the Godhead” as St. Basil the Great puts it (On the Holy Spirit 45). The emphasis here on communion acts as a safeguard against any tendency to see the three persons as simply different manifestations of the one nature; if they were simply different modes in which the one God appears, then such an act of communion would not be possible. The similar way of expressing the divine unity is in terms of “coinherence” (perichoresis): the Father, Son and Holy Spirit indwell in one another, totally transparent and interpenetrated by the other two. This idea clearly stems from Christ’s words in the Gospel of John: I am in the Father and the Father in Me (14:11). Having the Father dwelling in HIm in this way, Christ reveals to us the Father, He is the image of the invisible God (Colossians 1:15).
The third way in which the total unity of the Father, Son and Holy Spirit is manifest is in their unity of work or activity. Unlike three human beings who, at best, can only cooperate, the activity of the Father, Son and Holy Spirit is one. God works, according to the image of St. Irenaeus, with His two Hands, the Son and the Spirit. More importantly, “the work of God,” according to St. Irenaeus, “is the fashioning of man” into the image and likeness of God (Against the Heretics 5.15.2), a work which embraces, inseparably, both creation and salvation, for it is only realized in and by the crucified and risen One: the will of the Father is effected by the Son in the Spirit.
Such, then, is how the Greek Fathers, following Scripture, maintained that there is but one God, whose Son and Spirit are equally God, in a unity of essence and of existence, without compromising the uniqueness of the one true God.
The question remains, of course, concerning the point of such reflection. There are two directions for answering the question. There are two directions for answering the question. Theological reflection is, to begin with, an attempt to answer the central question posed by Christ Himself: Who do you say that I am? (Matthew 16:15). Yet at the same time, it also indicates the destiny to which we are also called, the glorious destiny of those who suffer with Christ, who have been conformed to the image of His Son, the first-born, of many brethren (Romans 8:29). What Christ is as first-born, we too may enjoy, in Him, when we also enter into the communion of love: The glory which though hast given me, I have given to them, that they may be one even as we are one (John 17:22).