16 Since, therefore, the words of the Apostle, One God the Father, from Whom are all things, and one Jesus Christ, our Lord, through Whom are all things, form an accurate and complete confession concerning God, let us see what Moses has to say of the beginning of the world. His words are, And God said, Let there be a firmament in the midst of the water, and let it divide the water from the water. And it was so, and God made the firmament and God divided the water through the midst. Here, then, you have the God from Whom, and the God through Whom.
If you deny it, you must tell us through whom it was that God's work in creation was done, or else point for your explanation to an obedience in things yet uncreated, which, when God said Let there be a firmament, impelled the firmament to establish itself. Such suggestions are inconsistent with the clear sense of Scripture. For all things, as the Prophet says, were made out of nothing; it was no transformation of existing things, but the creation into a perfect form of the non-existent.
Through whom? Hear the Evangelist: All things were made through Him. If you ask Who this is, the same Evangelist will tell you: In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through Him. If you are minded to combat the view that it was the Father Who said, Let there be a firmament, the prophet will answer you: He spoke, and they were made; He commanded, and they were created. The recorded words, Let there be a firmament, reveal to us that the Father spoke.
But in the words which follow, And it was so, in the statement that God did this thing, we must recognise the Person of the Agent. He spoke, and they were made; the Scripture does not say that He willed it, and did it. He commanded, and they were created; you observe that it does not say they came into existence, because it was His pleasure. In that case there would be no office for a Mediator between God and the world which was awaiting its creation.
God, from Whom are all things, gives the order for creation which God, through Whom are all things, executes. Under one and the same Name we confess Him Who gave and Him Who fulfilled the command. If you dare to deny that God made is spoken of the Son, how do you explain All things were made through Him? Or the Apostle's words, One Jesus Christ, our Lord, through Whom are all things? Or, He spoke, and they were made? If these inspired words succeed in convincing your stubborn mind, you will cease to regard that text, Hear, O Israel, the Lord your God is One, as a refusal of Divinity to the Son of God, since at the very foundation of the world He Who spoke it proclaimed that His Son also is God.
But let us see what increase of profit we may draw from this distinction of God Who commands and God Who executes. For though it is repugnant even to our natural reason to suppose that in the words, He commanded, and they were made, one single and isolated Person is intended, yet, for the avoidance of all doubts, we must expound the events which followed upon the creation of the world.
Source: On the Trinity (New Advent)