This is part 2 of 3. Part 1 is here. Part 3 is here.
Ἓν μὲν χαλεπῆς νόσου καὶ δυσιάτου, ποσθένης, ἀπαλλαγήν, ἣν ἄνθρακα καλοῦσιν, ἀπὸ τοῦ καίειν ἐντυφόμενον, ὡς οἶμαι, ταύτης τῆς προσηγορίας τυχόντα, ὅπερ εὐκολώτερον τοῖς ἀκροποσθίας ἔχουσιν ἐγγίνεται· δεύτερον δὲ τὴν δι’ ὅλου τοῦ σώματος καθαριότητα πρὸς τὸ ἁρμόττον τάξει ἱερωμένῃ, παρὸ καὶ ξυρῶνται τὰ σώματα προσυπερβάλλοντες οἱ ἐν Αἰγύπτῳ τῶν ἱερέων· ὑποσυλλέγεται γὰρ καὶ ὑποστέλλει καὶ θριξὶ καὶ ποσθίαις ἔνια τῶν ὀφειλόντων καθαίρεσθαι· τρίτον δὲ τὴν πρὸς καρδίαν ὁμοιότητα τοῦ περιτμηθέντος μέρους· πρὸς γὰρ γένεσιν ἄμφω παρεσκεύασται, τὸ μὲν ἐγκάρδιον πνεῦμα νοημάτων, τὸ δὲ γόνιμον ὄργανον ζῴων· ἐδικαίωσαν γὰρ οἱ πρῶτοι τῷ ἀφανεῖ καὶ κρείττονι, δι’ οὗ τὰ νοητὰ συνίσταται, τὸ ἐμφανὲς καὶ ὁρατόν, ᾧ τὰ αἰσθητὰ γεννᾶσθαι πέφυκεν, ἐξομοιῶσαι· τέταρτον δὲ καὶ ἀναγκαιότατον τὴν πρὸς πολυγονίαν παρασκευήν· λέγεται γὰρ ὡς εὐοδεῖ τὸ σπέρμα μήτε σκιδνάμενον μήτε περιρρέον εἰς τοὺς τῆς ποσθίας κόλπους· ὅθεν καὶ τὰ περιτεμνόμενα τῶν ἐθνῶν πολυγονώτατα καὶ πολυανθρωπότατα εἶναι δοκεῖ.
(Philo, Peri tōn en merei diatagmatōn 1.4-7)
One is that it secures exemption from the severe and almost incurable malady of the prepuce called anthrax or carbuncle, so named, I believe from the slow fire which it sets up and to which those who retain the foreskin are more susceptible. Secondly, it promotes the cleanliness of the whole body as befits the consecrated order, and therefore the Egyptians carry the practice to a further extreme and have the bodies of their priests shaved. For some substances which need to be cleared away collect and secrete themselves both in the hair and the foreskin. Thirdly, it assimilates the circumcised member to the heart. For as both are framed to serve for generation, thought being generated by the spirit force in the heart, living creatures by the reproductive organ, the earliest men held that the unseen and superior element to which the concepts of the mind owe their existence should have assimilated to it the visible and apparent, the natural parent of the things perceived by sense. The fourth and most vital reason is its adaptation to give fertility of offspring, for we are told that its causes semen to travel aright without being scattered or dropped into the folds of the foreskin, and therefore the circumcised nations appear the most prolific and populous. (tr. Francis Henry Colson)