38 Now that He Who is God over all is also Spirit inseparable from the Father, learn also from that very utterance of the Apostle, of which we are now speaking. For when he confessed one God the Father from Whom are all things, and one Lord Jesus Christ through Whom are all things; what difference, I ask, did he intend by saying that all things are from God and that all things are through Christ? Can He possibly be regarded as of a nature and spirit separable from Himself, He from Whom and through Whom are all things?
For all things have come into being through the Son out of nothing, and the Apostle has referred them to God the Father, From Whom are all things, but also to the Son, through Whom are all things. And I find here no difference, since by Each is exercised the same power. For if with regard to the subsistence of the universe it was an exact sufficient statement that things created are from God, what need was there to state that the things which are from God are through Christ, unless it be one and the same thing to be through Christ and from God?
But as it has been ascribed to Each of Them that They are Lord and God in such wise that each title belongs to Both, so too from Whom and through Whom is here referred to Both; and this to show the unity of Both, not to make known God's singleness. The language of the Apostle affords no opening for wicked error, nor is his faith too exalted for careful statement. For he has guarded himself by those specially appropriate words from being understood to mean two Gods or a solitary God: for while he rejects oneness of person he yet does not divide the unity of Godhead.
For this from Whom are all things and through Whom are all things, although it did not posit a solitary Deity in the sole possession of majesty, must yet set forth One not different in efficiency, since from Whom are all things and through Whom are all things must signify an Author of the same nature engaged in the same work. He affirms, moreover, that Each is properly of the same nature. For after announcing the depth of the riches and wisdom and knowledge of God, and after asserting the mystery of His inscrutable judgments and avowing our ignorance of His ways past finding out, he has yet made use of the exercise of human faith, and rendered this homage to the depth of the unsearchable and inscrutable mysteries of heaven, For of Him and through Him and in Him are all things: to Him be glory for ever.
Amen</em>. He employs to indicate the one nature, that which cannot but be the work of one nature.
Source: On the Trinity (New Advent)