As we previously observed, it is difficult for us to understand the Holy Trinity completely. However, it is necessary to say certain things about the Holy Trinity and about the special attributes of the three Persons.
The first thing to keep in mind is that the Holy Trinity is always united. Christ in His high priestly prayer prayed for the unity of the world and gave us an example and a model: He said, "That they may be one, even as We are One" (John, 17:22). What does We mean? The Father, the Son, and the Holy Spirit. The Three Persons of the Holy Trinity.
And what does this mean? Is it possible that the three Persons are really the same Person and that Person presents Himself, appropriately to the situation, as the Father or the Son or the Holy Spirit? No. The Holy Trinity is one in essence and inseparable, one undivided Being. It is of one substance. The three Persons are undivided, but distinct. We must not confuse Them or separate Them. They co-inhere in one another; that is to say, One fits inside the Other. The Father fits in and is always inside the Son and the Holy Spirit. The Son fits in and is always inside the Father and the Holy Spirit. The Holy Spirit fits in and is always inside the Father and the Son. Can the human mind grasp this? No. That is why we previously said that there are things "beyond logic," above our own logic. However, just because it is beyond logic and above our own mental capacities does not mean that what has been revealed to us by God is not true. It is precisely as God has revealed it to us, because He alone knows Himself. This is seen more clearly in the words of Christ, when He said, "He that has seen Me has seen the Father. . . . I am in the Father and the Father in Me" (John, 14:9-10).
Although this is the way things are, there are nevertheless certain individual qualities of the three Persons of the Holy Trinity. The Father is unborn. The Son is born of the Father. The Holy Spirit proceeds from the Father. The Father is the beginning, but the Son is co-existent and the Holy Spirit, also. In other words, the Father did not exist before the Son and the Holy Spirit, nor is the Father superior to the other two Persons of the Holy Trinity. The three Persons are equal. This is all very difficult to comprehend with human rationality. St. John of Damascus manages to explain matters. He says that because the Son is born of the Father does not mean that He is separate, as the light is not separated from the fire. The fire gives birth to light simultaneously. That is why we cannot say that the fire existed before the light. The Son is born of the Father but simultaneously and eternally and is never separate. The same is true of the Holy Spirit, proceeding from the Father but simultaneously and eternally and never separated.
Let us pay attention also to this. When we say that the substance of the three Persons of the Holy Trinity is the same, we do not mean that this substance is divided. It is not cut up into three pieces, for each Person to take one piece. No. The Father is infinite, and He has all of the infinite divine substance. And the Son is infinite and has all of the infinite divine substance. And the Holy Spirit is infinite and has all of the infinite divine substance. We cannot say that the substance of the Father exists up to a certain point and that it ends there; and that from there begins the substance of the Son; and that from where the substance of the Son ends, there begins the substance of the Holy Spirit. No. That would all be heresy. Wherever the substance of the Father exists [i.e., everywhere] there exists the substance of the Son and of the Holy Spirit. Wherever the Father exists [everywhere], there exists the Son and the Holy Spirit, and vice-versa. Wherever the Son exists [everywhere], the Father and the Holy Spirit exist. Wherever the Holy Spirit exists [everywhere], there exist the Father and the Son.
Such are the particular characteristics of the three Persons of the Holy Trinity. The Father is without beginning and is the beginning. The Son is co-existent with the Father, as we have previously explained, but is born of the Father simultaneously and eternally. The Holy Spirit is co-existent with the Father, but proceeds from the Father simultaneously and eternally.
Here we have to add that the Holy Spirit proceeds only from the Father, not "and from the Son" as the Roman Catholics and the Protestants say. Christ has told us this: "The Spirit of Truth that proceeds from the Father" (John, 15-26). And so the Second Ecumenical Council decreed, "[I believe in] the Holy Spirit . . . Who proceeds from the Father." The Third Ecumenical Council decreed that no one can add or delete anything from the Creed. Pope Leo III had the Creed engraved on silver plates without the addition "and from the son," and at the bottom he added, "Let him be anathematized who adds even a small jot to this Creed." However, the Roman Catholics and Protestants added "and from the Son" to the Creed, contrary to the teaching of Christ and the decision of the Second Ecumenical Council and the anathema of Pope Leo III. But they will return to the Orthodox faith.Father without beginning, Son co-existent, born of the Father, Holy Spirit co-existent and proceeding from the Father, Trinity of One Essence, Undivided, United, Inseparable, and Distinct, hear our prayer and the groaning of our souls. Keep us in our Orthodox faith. Have those who have adulterated our faith recover and return. Make them accept the complete teaching of the Holy Scriptures and Holy Tradition. Have them follow the infallible decisions of the Ecumenical Councils. Make all people become one flock under One Shepherd, Christ. Have us be one as You are, Father, Son, and Holy Spirit, One True God.