Genesis 17:11

And ye shall be circumcised in the flesh of your foreskin; and it shall be a token of a covenant betwixt Me and you

Onkelos Targum
 וְתִגְזְרוּן יָת בִּסְרָא דְּעֻרְלַתְכוֹן וִיהֵי לְאָת קְיָם בֵּין מֵימְרִי וּבֵינֵיכוֹן

Philo, Special Laws 1.1-2.11
We must now proceed to consider the particular commands as we read them in the subsequent passages of the holy scriptures; and we will begin with that which is turned into ridicule by people in general. (2) The ordinance of circumcision of the parts of generation is ridiculed, though it is an act which is practised to no slight degree among other nations also, and most especially by the Egyptians, who appear to me to be the most populous of all nations, and the most abounding in all kinds of wisdom. (3) In consequence of which it would be most fitting for men to discard childish ridicule, and to investigate the real causes of the ordinance with more prudence and dignity, considering the reasons why the custom has prevailed, and not being precipitate, so as without examination to condemn the folly of mighty nations, recollecting that it is not probable that so many myriads should be circumcised in every generation, mutilating the bodies of themselves and of their nearest relations, in a manner which is accompanied with severe pain, without adequate cause; but that there are many reasons which might encourage men to persevere and continue a custom which has been introduced by previous generations, and that these are from reasons of the greatest weight and importance. (4) First of all, that it is a preventive of a painful disease, and of an affliction difficult to be cured, which they call a carbuncle; {1} because, I imagine, when it becomes inflamed it burns; from which fact it has derived that appellation. And this disease is very apt to be engendered among those who have not undergone the rite of circumcision. (5) Secondly, it secures the cleanliness of the whole body in a way that is suited to the people consecrated to God; with which object the Egyptian priests, being extravagant in their case, shave the whole of their bodies; for some of these evils which ought to be got rid of are collected in and lodge under the hair and the prepuce. (6) Thirdly, there is the resemblance of the part that is circumcised to the heart; for both parts are prepared for the sake of generation; for the breath contained within the heart is generative of thoughts, and the generative organ itself is productive of living beings. Therefore, the men of old thought it right to make the evident and visible organ, by which the objects of the outward senses are generated, resemble that invisible and superior part, by means of which ideas are formed. (7) The fourth, and most important, is that which relates to the provision thus made for prolificness; for it is said that the seminal fluid proceeds in its path easily, neither being at all scattered, nor flowing on its passage into what may be called the bags of the prepuce. On which account those nations which practise circumcision are the most prolific and the most populous.

II. (8) These considerations have come to our ears, having been discussed of old among men of divine spirit and wisdom, who have interpreted the writings of Moses in no superficial or careless manner. But, besides what has been already said, I also look upon circumcision to be a symbol of two things of the most indispensable importance. (9) First of all, it is a symbol of the excision of the pleasures which delude the mind; for since, of all the delights which pleasure can afford, the association of man with woman is the most exquisite, it seemed good to the lawgivers to mutilate the organ which ministers to such connections; by which rite they signified figuratively the excision of all superfluous and excessive pleasure, not, indeed, of one only, but of all others whatever, though that one which is the most imperious of all. (10) The second thing is, that it is a symbol of a man's knowing himself, and discarding that terrible disease, the vain opinion of the soul; for some men, like good statuaries, have boasted that they can make that most beautiful animal, man; and, being puffed up with arrogance, have deified themselves, hiding from sight the true cause of the creation of all things namely, God, although they might have corrected that error from a consideration of other persons among whom they live; (11) for there are among them many men who have no children, and many barren women whose connections lead to nothing, so that they grow old in childlessness. We must therefore eradicate evil opinions from the mind, and all other ideas which are not devoted to God. This, then, is enough to say on these subjects.