Guide for the Perplexed, by Moses Maimonides, Friedländer tr. [1904], at sacred-texts.com
THE Hebrew kanaf is a homonym; most of its meanings are metaphorical. Its primary signification is "wing of a flying creature," e.g., "Any winged (kanaf) fowl that flieth in the air" (Deut. iv. 17).
The term was next applied figuratively to the wings or comers of garments comp. "upon the four corners (kanfoth) of thy vesture" (ib. xxii. 12).
It was also used to denote the ends of the inhabited part of the earth, and the corners that are most distant from our habitation. Comp. "That it might take hold of the ends (kanfoth) of the earth" (Job xxxviii. 13); "From the uttermost part (kenaf) of the earth have we heard songs" (Isa. xxiv. 16).
Ibn Ganaḥ (in his Book of Hebrew Roots) says that kenaf is used in the sense of "concealing," in analogy with the Arabic kanaftu alshaian, "I have hidden something," and accordingly explains, Isaiah xxx. 20, "And thy teacher will no longer be hidden or concealed." It is a good explanation, and I think that kenaf has the same meaning in Deuteronomy xxiii. 1, "He shall not take away the cover (kenaf) of his father"; also in, "Spread, therefore, thy cover (kenafeka) over thine handmaid" (Ruth iii. 9). In this sense, I think, the word is figuratively applied to God and to angels (for angels are not corporeal, according to my opinion, as I shall explain). Ruth ii. 12 must therefore be translated "Under whose protection (kenafav) thou art come to trust"; and wherever the word occurs in reference to angels, it means concealment. You have surely noticed the words of Isaiah (Isa. vi. 2), "With twain he covered his face, and with twain he covered his feet." Their meaning is this: The cause of his (the angel's) existence is hidden and concealed; this is meant by
the covering of the face. The things of which he (the angel) is the cause, and which are called "his feet" (as I stated in speaking of the homonym regel, are likewise concealed: for the actions of the intelligences are not seen, and their ways are, except after long study, not understood, on account of two reasons--the one of which is contained in their own properties, the other in ourselves: that is to say, because our perception is imperfect and the ideals are difficult to be fully comprehended. As regards the phrase "and with twain he flieth," I shall explain in a special chapter (xlix.) why flight has been attributed to angels.