THE MYSTERIES OF THE GREEK ALPHABET
Upsilon is known as Pythagoras’ letter, or the Samian letter, because Pythagoras used it as an emblem of the path of virtue or vice. As the Roman writer Persius wrote in Satire III:
“..and the letter which spreads out into Pythagorean branches has pointed out to you the steep path which rises on the right.”
Lactantius (c240-320 AD) said also,
For they say that the course of human life resembles the letter Y, because every one of men, when he has reached the threshold of early youth, and has arrived at the place ‘where the way divides itself into two parts’, is in doubt, and hesitates, and does not know to which side he should rather turn himself.
Lactantius, The Divine Institutes. pp. Book VI Chapter III.
These ideas seem to have an ancient root, one common to early Jewish Kabbala and Christian mystical number symbolism.
On this see See Guy Strouma, ‘The Mystery of the Greek Letters: A Byzantine Kabbalah’ (available through academia.edu) from which the following excerpt comes:
The Coptic Text of the ‘Mysteries…‘ exists in other versions. Most commentaries refer to it as ”The Mystery of the Greek Letters’. Its most recent translation was into English. Antony Alcock offered the translation in three guest posts to Alin Suciu’s blog ‘Patristics, Apocrypha, Coptic Literature and Manuscripts’: Part I (April 9th., 2013), Part II (April 23rd., 2013); and Part III (May 7th., 2013).
Alcock took as his text a 14th cent. Sahidic Coptic manuscript now in the Bodleian Library, Oxford as MS Huntington 393. The library attibutes the manuscript to one Atasios, who is said to have written it in 1109 AM (1393 AD). The same manuscript’s text was earlier published (with translation and notes) by Adolphe Hebbelynck in Le Muséon vol. 19 (1900) in three sections: pp. 5-36, 105-136 and 259-300 and in vol. 20 (1901) in two sections: pp. 5-33 and 369-415, together with 3 plates. Alcock intended to offer his English translation “also .. in 5 parts, following Hebbelynck’s arrangement.”
Roger Pearce has offered Alock’s pdfs through his own website, but doesn’t permit direct linking. It was there, however, that Siciu commented (under a post dated April 9th., 2013) that “The original Greek version of this text was published in 2007. See C. Bandt, ‘Der Traktat “Vom Mysterium der Buchstaben”: Kritischer Text mit Einführung’, Übersetzung und Anmerkungen (Texte und Untersuchungen), 162; Berlin: Walter de Gruyter, (2007).