The first clause, "All things were made through him," is used to show three things concerning the Word. First, according to Chrysostom, to show the equality of the Word to the Father. For as stated earlier, the error of Arius was rejected by the Evangelist when he showed the coeternity of the Son with the Father by saying, “He was in the beginning with God.” Here he excludes the same error when he shows the omnipotence of the Son, saying, All things were made through him. For to be the principle of all the things that are made is proper to the great omnipotent God, as the Psalm (134:6) says, “Whatever the Lord wills he does, in heaven and on earth.” Thus the Word, through whom all things were made, is God, great and coequal to the Father.
Secondly, according to Hilary, this clause is used to show the coeternity of the Word with the Father. For since someone might understand the earlier statement, “In the beginning was the Word,” as referring to the beginning of creatures, i.e., that before there were any creatures there was a time in which the Word did not exist, the Evangelist rejects this by saying, All things were made through him. For if all things were made through the Word, then time was also. From this we can form the following argument: If all time was made through him, there was no time before him or with him, because before all these, he was. Therefore they [the Son and the Father] are eternally coeternal.
Thirdly, according to Augustine, this clause is used to show the consubstantiality of the Word with the Father. For if all things were made through the Word, the Word himself cannot be said to have been made; because, if made, he was made through some Word, since all things were made through the Word. Consequently, there would have been another Word through whom was made the Word of whom the Evangelist is speaking. This Word, through whom all things are made, we call the only begotten Son of God, because he is neither made nor is he a creature. And if he is not a creature, it is necessary to say that he is of the same substance with the Father, since every substance other than the divine essence is made. But a substance that is not a creature is God. And so the Word, through whom all things were made, is consubstantial with the Father, since he is neither made, nor is he a creature.
And so in saying "All things were made through him," you have, according to Chrysostom, the equality of the Word with the Father; the coeternity of the Word with the Father, according to Hilary; and the consubstantiality of the Word with the Father, according to Augustine.
Thomas Aquinas, Commentary on the Gospel of John, Chapter 1, Lecture 2.