Origen a.d. 185–254
From all which we learn that the person of the Holy Spirit was of such authority and dignity, that saving baptism was not complete except by the authority of the most excellent Trinity of them all, i.e., by the naming of Father, Son, and Holy Spirit, and by joining to the unbegotten God the Father, and to His only-begotten Son, the name also of the Holy Spirit.
. . .
Nevertheless it seems proper to inquire what is the reason why he who is regenerated by God unto salvation has to do both with Father and Son and Holy Spirit, and does not obtain salvation unless with the co-operation of the entire Trinity; and why it is impossible to become partaker of the Father or the Son without the Holy Spirit.
Origen De Principiis. Book I Chapter III
But in our desire to show the divine benefits bestowed upon us by Father, Son, and Holy Spirit, which Trinity is the fountain of all holiness, we have fallen, in what we have said, into a digression, having considered that the subject of the soul, which accidentally came before us, should be touched on, although cursorily, seeing we were discussing a cognate topic relating to our rational nature. We shall, however, with the permission of God through Jesus Christ and the Holy Spirit, more conveniently consider in the proper place the subject of all rational beings, which are distinguished into three genera and species.
Origen De Principiis. Book I Chapter IV
For the end is always like the beginning: and, therefore, as there is one end to all things, so ought we to understand that there was one beginning; and as there is one end to many things, so there spring from one beginning many differences and varieties, which again, through the goodness of God, and by subjection to Christ, and through the unity of the Holy Spirit, are recalled to one end, which is like unto the beginning: all those, viz., who, bending the knee at the name of Jesus, make known by so doing their subjection to Him: and these are they who are in heaven, on earth, and under the earth: by which three classes the whole universe of things is pointed out, those, viz., who from that one beginning were arranged, each according to the diversity of his conduct, among the different orders, in accordance with their desert; for there was no goodness in them by essential being, as in God and His Christ, and in the Holy Spirit. For in the Trinity alone, which is the author of all things, does goodness exist in virtue of essential being; while others possess it as an accidental and perishable quality, and only then enjoy blessedness, when they participate in holiness and wisdom, and in divinity itself.
Origen De Principiis. Book I Chapter VI
After these points, now, we proved to the best of our power in the preceding pages that all things which exist were made by God, and that there was nothing which was not made, save the nature of the Father, and the Son, and the Holy Spirit; and that God, who is by nature good, desiring to have those upon whom He might confer benefits, and who might rejoice in receiving His benefits, created creatures worthy (of this), i.e., who were capable of receiving Him in a worthy manner, who, He says, are also begotten by Him as his sons. He made all things, moreover, by number and measure. For there is nothing before God without either limit or measure. For by His power He comprehends all things, and He Himself is comprehended by the strength of no created thing, because that nature is known to itself alone. For the Father alone knoweth the Son, and the Son alone knoweth the Father, and the Holy Spirit alone searcheth even the deep things of God.
Origen De Principiis. Book IV Chapter I.35
If the heavenly virtues, then, partake of intellectual light, i.e., of divine nature, because they participate in wisdom and holiness, and if human souls, have partaken of the same light and wisdom, and thus are mutually of one nature and of one essence,—then, since the heavenly virtues are incorruptible and immortal, the essence of the human soul will also be immortal and incorruptible. And not only so, but because the nature of Father, and Son, and Holy Spirit, whose intellectual light alone all created things have a share, is incorruptible and eternal, it is altogether consistent and necessary that every substance which partakes of that eternal nature should last for ever, and be incorruptible and eternal, so that the eternity of divine goodness may be understood also in this respect, that they who obtain its benefits are also eternal. But as, in the instances referred to, a diversity in the participation of the light was observed, when the glance of the beholder was described as being duller or more acute, so also a diversity is to be noted in the participation of Father, Son, and Holy Spirit, varying with the degree of zeal or capacity of mind.
Origen De Principiis. Book IV Chapter I.36
Dionysius, Bishop of Alexandria a.d. 200–265
The individual names uttered by me can neither be separated from one another, nor parted. I spoke of the Father, and before I made mention of the Son I already signified Him in the Father. I added the Son; and the Father, even although I had not previously named Him, had already been absolutely comprehended in the Son. I added the Holy Spirit; but, at the same time, I conveyed under the name whence and by whom He proceeded. But they are ignorant that neither the Father, in that He is Father, can be separated from the Son, for that name is the evident ground of coherence and conjunction; nor can the Son be separated from the Father, for this word Father indicates association between them. And there is, moreover, evident a Spirit who can neither be disjoined from Him who sends, nor from Him who brings Him. How, then, should I who use such names think that these are absolutely divided and separated the one from the other?
(After a few words he adds:—)
Thus, indeed, we expand the indivisible Unity into a Trinity; and again we contract the Trinity, which cannot be diminished, into a Unity.
(From the Same Second Book.)
In the beginning was the Word. But that was not the Word which produced the Word. For “the Word was with God.” The Lord is Wisdom; it was not therefore Wisdom that produced Wisdom; for “I was that” says He, “wherein He delighted.” Christ is truth; but “blessed,” says He, “is the God of truth.”
(The Conclusion of the Entire Treatise.)
In accordance with all these things, the form, moreover, and rule being received from the elders who have lived before us, we also, with a voice in accordance with them, will both acquit ourselves of thanks to you, and of the letter which we are now writing. And to God the Father, and His Son our Lord Jesus Christ, with the Holy Spirit, be glory and dominion for ever and ever. Amen.
The Works of Dionysius. Extant Fragments. Part I Chapter IV
Cyprian a.d. 200–258
Finally, when, after the resurrection, the apostles are sent by the Lord to the heathens, they are bidden to baptize the Gentiles “in the name of the Father, and of the Son, and of the Holy Ghost.” How, then, do some say, that a Gentile baptized without, outside the Church, yea, and in opposition to the Church, so that it be only in the name of Jesus Christ, everywhere, and in whatever manner, can obtain remission of sin, when Christ Himself commands the heathen to be baptized in the full and united Trinity?
Epistle LXXII.5.18
Novatian a.d. 210–280
And now, indeed, concerning the Father, and the Son, and the Holy Spirit, let it be sufficient to have briefly said thus much, and to have laid down these points concisely, without carrying them out in a lengthened argument. For they could be presented more diffusely and continued in a more expanded disputation, since the whole of the Old and New Testaments might be adduced in testimony that thus the true faith stands. But because heretics, ever struggling against the truth, are accustomed to prolong the controversy of pure tradition and Catholic faith, being offended against Christ; because He is, moreover, asserted to be God by the Scriptures also, and this is believed to be so by us; we must rightly—that every heretical calumny may be removed from our faith—contend, concerning the fact that Christ is God also, in such a way as that it may not militate against the truth of Scripture; nor yet against our faith, how there is declared to be one God by the Scriptures, and how it is held and believed by us.
A Treatise of Novatian Concerning the Trinity. Chapter XXX.
Alexander, Bishop of Alexandria a.d. 273–326
Therefore, when the holy prophets, and all, as I have said, who righteously and justly walked in the law of the Lord, together with the entire people, celebrated a typical and shadowy Passover, the Creator and Lord of every visible and invisible creature, the only-begotten Son, and the Word co-eternal with the Father and the Holy Spirit, and of the same substance with them, according to His divine nature, our Lord and God, Jesus Christ, . .
Epistles on the Arian Heresy And the Deposition of Arius. Chapter I.7
Therefore to the unbegotten Father, indeed, we ought to preserve His proper dignity, in confessing that no one is the cause of His being; but to the Son must be allotted His fitting honour, in assigning to Him, as we have said, a generation from the Father without beginning, and allotting adoration to Him, so as only piously and properly to use the words, “He was,” and “always,” and “before all worlds,” with respect to Him; by no means rejecting His Godhead, but ascribing to Him a similitude which exactly answers in every respect to the Image and Exemplar of the Father. But we must say that to the Father alone belongs the property of being unbegotten, for the Saviour Himself said, “My Father is greater than I.” And besides the pious opinion concerning the Father and the Son, we confess to one Holy Spirit, as the divine Scriptures teach us; who hath inaugurated both the holy men of the Old Testament, and the divine teachers of that which is called the New.
Epistles on the Arian Heresy And the Deposition of Arius. Chapter I.12