11 And savoring as these men always did of the earth, and ever hearing and answering according to the flesh, what did they say to Him? “Who are you?” For when you said, “If you believe not that I am,” thou did not tell us what thou were. Who are you, that we may believe? He answered “The Beginning.” Here is the existence that [always] is. The beginning cannot be changed: the beginning is self-abiding and all-originating; that is, the beginning, to which it has been said, “But thou Yourself art the same, and Your years shall not fail.” “The beginning,” He said, “for so I also speak to you.”
Believe me [to be] the beginning, that you may not die in your sins. For just as if by saying, “Who are you?” they had said nothing else than this, What shall we believe you to be? He replied, “The beginning;” that is, Believe me [to be] the “beginning.” For in the Greek expression we discern what we cannot in the Latin. For in Greek the word “beginning” (principium, ἀρχή), is of the feminine gender, just as with us “law” (lex) is of the feminine gender, while it is of the masculine (νόμος) with them; or as “wisdom” (sapientia, σοφία) is of the feminine gender with both.
It is the custom of speech, therefore, in different languages to vary the gender of words, because in things themselves there is no place for the distinction of sex. For wisdom is not really female, since Christ is the Wisdom of God, and Christ is termed of the masculine gender, wisdom of the feminine. When then the Jews said, “Who are you?” He, who knew that there were some there who should yet believe, and therefore had said, Who are you? That so they might come to know what they ought to believe regarding Him, replied, “The beginning:” not as if He said, I am the beginning; but as if He said, Believe me [to be] the beginning.
Which, as I said, is quite evident in the Greek language, where beginning (ἀρχή) is of the feminine gender. Just as if He had wished to say that He was the Truth, and to their question, “Who are you?” had answered, Veritatem [the Truth]; when to the words, “Who are you?” He evidently ought to have replied, Veritas [the Truth]; that is, I am the Truth. But His answer had a deeper meaning, when He saw that they had put the question, “Who are you?” in such a way as to mean, Having heard from you, “If you believe not that I am,” what shall we believe you to be?
To this He replied, “The beginning:” as if He said, Believe me to be the beginning. And He added “for [as such] I also speak to you;” that is, having humbled myself on your account, I have condescended to such words. For if the beginning as it is in itself had remained so with the Father, as not to receive the form of a servant and speak as man with men; how could they have believed in Him, since their weak hearts could not have heard the Word intelligently without some voice that would appeal to their senses? Therefore, said He, believe me to be the beginning; for, that you may believe, I not only am, but also speak to you. But on this subject I have still much to say to you; may it therefore please your Charity that we reserve what remains, and by His gracious aid deliver it tomorrow.
Source: Tractates on the Gospel of John (New Advent)