The other pole of the Church’s experience is that Father, Son, and Holy Spirit, mysteriously and paradoxically, are not three gods, but a single God. The Church theologized upon this experience by saying that Father, Son, and Holy Spirit all share the same “substance,” or “essence.” By “essence,” we mean: that without which a thing would not be what it is; or in fact would not be, period.
We can have no idea what God has or is, such that if He did not have It or be It, He would not be God, would not even be. But whatever that is, we call It His Essence. “The Nature of Divinity,” we might also say. ( “Essence”, “substance”, and “nature” are often used by theologians interchangeably.) Whatever it is, all Three of His hypostases alike have it. Each has, so to speak, all of it, not merely a share in it. That is, each is fully God, not a third of God. The Father confers all of His own “substance” upon the Son as He is begotten and upon the Holy Spirit as He proceeds. We could say, loosely speaking, that the Father makes them to have His own kind of Being. (More strictly speaking, God is neither a Being nor has being, but is the Creator of being.)
(This is a little easier for our minds to grasp if we consider that each human person is a unique hypostasis of one nature, namely, human nature, which is the same in every one of us – although we divide human nature among us, each having, so to speak a piece of the reality, whereas the Persons of the Holy Trinity each have the Divine Essence in its entirety.)
St. Photios the Great (Mystagogy of the Holy Spirit, 46) explains how it is that the Hypostases are not confused and the Essence is not divisible:
…each hypostasis of the consubstantial and divine Trinity is ineffably united to each other in an inseparable communion of nature, but each maintains His specific and unique characteristic properties by distinction of the hypostases. This distinction allows no room for confusion … because the communion of nature does not permit any severance or division, nor are the properties which distinguish each of the three permitted to be mingled into any fusion.
The Son and the Holy Spirit are of one Essence (are “consubstantial”) with the Father because They originate from the Father, Who confers His own Essence upon the Them. It is very important that the Father causes the Holy Trinity, and not the divine Essence. Essences do not cause or act; they simply are. The Father, Son, and Holy Spirit act. The Father, not the divine Essence, both causes the Hypostases and is the principle of their unity.
Because they all are of one Essence (or “Substance”), the Three Hypostases are equal in dignity, in majesty, in rank, and are worshipped equally as one and inseparable.
The inseparability of the Three is as important as their Threeness. To theologize in a way that separates any Hypostasis from another is to give up monotheism. There is no such thing as one having a will contrary to that of another’s, or of one acting against another, or of one having a different disposition or attitude than another. There is no opposition of any kind within the Holy Trinity. Whatever the Three are, they are it together as One. Whatever they have, they have in common; whatever we say they think or say or do, we must say they think or say or do jointly. Otherwise, we end up with three gods. Further, we end up, in practice, loving one of the three gods more than another, even though in Christianity this is a theoretical impossibility. Many people go around saying how much they love Jesus. How few exclaim how much they love the Father! And many people don’t even seem to know what to do with the Holy Spirit.
It is important, as always, that our theologizing begins with and is based upon our experience as Church, which is another way of saying, upon God’s self-revelation to us in history. In theologizing about the Holy Trinity, we begin by saying that in the real world, we have encountered Three who nevertheless, because of having all the same powers and energies, disclose Themselves as One. (We insist that God reveals Himself to us as He really is. He really is, in Himself, Three yet One; this is no mere appearance.)
Our concrete experience is not the other way around! That is, we have not, in the real world, encountered some nebulous philosophical entity called a “Oneness” or an “Essence” which, nevertheless (for what reason?) requires some threefold explanation. The latter approach changes theology from prayerful reflection upon Christian experience into philosophizing about impersonal abstractions (for what else is “Oneness” or “Essence”?). Such philosophizing leaves us with concepts only, divorced from our concrete reality. Religion thereby becomes a system of thought, an artifact of the human mind, an idol of our intellect, rather than real, heavenly yet down-to-earth, Life in Christ. That is how “Christian” religion, because of being abstracted from our concrete experience, eventually becomes irrelevant and breaks down altogether, collapsing into the materialism, secularism and meaninglessness which, in turn, in Europe and elsewhere, are not so gradually being replaced by Islam.
It is most emphatically not an Essence or a Nature we worship, or anything else impersonal; neither is the subject of our study or theologizing some ethereal Substance. Our God is the Son who came among us in flesh and blood, the Father He preached, of whom He is the exact Icon, and the Holy Spirit He sent: Father, Son, and Holy Spirit, the Trinity, one in Essence, undivided and indivisible. God is intensely personal.