¹ When speaking about God, dearest brothers, just as the desire to argue is greatly harmful, so too is the diligence of inquiry greatly beneficial. For in the former, the mind is hardened by obstinacy, while in the latter, the intellect is nourished by investigation. There, resistant unbelief delights in its own corruption, while here, obedient humility is rewarded with wisdom. Therefore, beloved brothers, prepare the sanctuary of your holy hearts as a vessel to receive the flowing waters of divine grace. And what we long to reveal regarding the mystery of the Holy Trinity and the divinity of the Holy Spirit, receive with silence and reverence. For we wish to confirm through the testimony of the Sacred Scriptures how the Holy Spirit can clearly be recognized as coequal with the Father and the Son in all divine powers.

² We read in the Old Testament: “In the beginning, God created the heavens and the earth, and the Spirit of God was hovering over the waters”. In God, recognize the Father; in the Beginning, understand the Son; and in the One hovering over the waters, acknowledge the Holy Spirit. Even then, I believe, the Spirit’s majestic presence over the waters prefigured the grace of baptism.

³ Furthermore, when creating humanity, God reveals the work not of one person alone but of three, through the threefold repetition of the divine name. For it is written: “Then God said: Let us make humankind in our image, according to our likeness”. Notice how the statement begins with a singular subject but proceeds with a plural response. “Then God said: Let us make humankind” — what does this mean, if not that the oneness of the divine essence speaks, while the power of the Trinity acts?

⁴ Observe how, in the creation of humanity, the name of God is invoked three times, signifying the three persons: “Then God said: Let us make humankind” — here, the Father speaks. “God created humankind” — here, the Son acts. “God blessed them” — here, the Holy Spirit bestows the blessing. Because of the three persons, the one divinity is repeated three times. In this passage, you can clearly discern the mystery of unity as well: the image of God and His likeness is given to each human being by the three persons, yet it remains one image. Consider carefully: God speaks as one, but He does not act as one; and again, He mixes the singular and the plural, for He does not say: “in our images and likenesses” nor “in my image and likeness”. By using the plural, He proclaims the Trinity, while by using the singular, He affirms the unity of the divine essence. Thus, in saying: “Let us make… in our image”, the number of persons is revealed. Yet in the singular phrase: “in the image and likeness”, the undivided divine essence is made known.

⁵ When God appeared to Abraham at the entrance of his tent, He wondrously revealed Himself to his eyes as three persons, though He was one. Abraham, aware of the divine majesty, worshiped the one God in the threefold manifestation. In the Psalms, the unity of the divine persons is also clearly expressed: “Do not cast me away from your presence, and do not take your Holy Spirit from me”. Here, the prophet, pleading with the Father, fears offending not only the Father but also the Son and the Holy Spirit. He says: “Do not cast me away from your presence” — the Son, as the image of the Father, is likewise understood as the presence or face of the Father. Therefore, we read: “Philip, whoever has seen me has seen the Father”. And again: “Where can I go from your Spirit? Or where can I flee from your presence?”. Take heed, you who doubt, of the perfect confession of the Trinity. The prophet addresses the Father, acknowledges the Son as the Father’s face, and proclaims the Holy Spirit as the one who fills all things.

⁶ Concerning the Son, the Lord also speaks to Moses, saying: “My face shall go before you”. The term face here refers both to the unity of the divine essence and to the co-eternity of the divine majesty. Isaiah also includes the Holy Spirit in the glory of the Trinity when he declares: “I saw the Lord seated on a high and lofty throne, and the seraphim stood around Him, calling out to one another: ‘Holy, holy, holy is the Lord God of hosts’”. And shortly after, he says: “Then I heard the voice of the Lord saying: ‘Go and say to this people: You will indeed hear but never understand; you will indeed see but never perceive’”. Thus, in both vision and proclamation, the prophet confesses the mystery of the triune God — the Lord of hosts, revealed in the threefold Sanctus of the seraphim, signifying the Father, the Son, and the Holy Spirit.

⁷ Let us at least believe the renowned herald of truth, Paul, when he declares that the Holy Spirit was the Lord of Hosts whom Isaiah saw and who spoke through Isaiah. But since the thrice-repeated exclamation resounds: “Holy, holy, holy,” let us consider whether this honour refers to the entire Trinity. When Isaiah says: “I saw the Lord of Hosts”, the Jews recognize this as a reference to the Father. However, the Evangelist John clearly asserts that it refers to the Son, when he says: “For this reason they could not believe, because Isaiah said: ‘He has blinded their eyes and hardened their heart.’ Isaiah said this because he saw His glory and spoke about Him”.

⁸ Now, when Isaiah also says: “And I heard the voice of the Lord saying: ‘Go and say to this people: You will indeed hear but never understand, and you will indeed see but never perceive’”, the Apostle Paul, as we have mentioned, confirms that this Lord is the Holy Spirit. You see, then, that the thrice-repeated “Holy, holy, holy” celebrates the entire Trinity. And just as there is no dissimilarity or difference in these three words, so too, in the power of the Trinity, there can be no division.

⁹ But you say: “From this, it is clearly recognized that the Holy Spirit is lesser, since He is called the finger of God.”Not so. Rather, when you hear it said of the Holy Spirit: “If I cast out demons by the finger of God”, you should understand that this demonstrates the unity of substance, not a diminishment of glory. It shows the harmony of operation, not a discrepancy in honour.

¹⁰ What then? Because the Holy Spirit is sometimes called the finger of God, is He therefore believed to be lesser than the Son and the Father? Flee from the error of such a persuasion! Consider whether, at times, this designation of the finger also encompasses both the Father and the Son. Let us remember that Scripture does not speak of only one finger when it says: “When I consider Your heavens, the work of Your fingers”. But you argue that this mention of fingers refers only to the Son and the Holy Spirit, indicating some form of duality. Do not attempt to claim this as referring to only two persons, for in another passage, Isaiah speaks specifically of three fingers, referring to the Trinity, when he says: “Who has measured the waters in the hollow of His hand and marked off the heavens with a span, enclosed the dust of the earth in a measure, and weighed the mountains in scales and the hills in a balance? Who has weighed the earth’s mass with three fingers?”.

¹¹ What could be clearer regarding the unity of the Trinity? What could be more evident? Do you not see that, in the mention of these three fingers, the equality of the one power is balanced on the scale of a hidden mystery? Therefore, as has been said, now that you have been instructed concerning the shared operation, do not doubt the equality of power. Thus, when Scripture says: “Who has weighed the earth’s mass with three fingers,” it specifically speaks of the cooperation of power and the unity of substance, which is shown to be one and the same in the three fingers.

¹² Although the Holy Spirit continually kindles your hearts to hear the word of God, so much so that your holy longing can scarcely be satisfied, it is nevertheless necessary to ensure that the preaching of God’s word is moderated in such a way that it may always be desired and can constantly increase within you.

¹³ Therefore, let what has already been spoken suffice for your charity. And since we have believed it fitting to reserve a portion of this sermon for you, if, according to your custom, you gather together a little earlier tomorrow, after completing the morning prayers without weariness, you will hear what has been deliberately kept back, through the grace of our Lord Jesus Christ, to whom belongs honour forever and ever. Amen.