Guide for the Perplexed, by Moses Maimonides, Friedländer tr. [1904], at sacred-texts.com
THE angels are likewise incorporeal: they are intelligences without matter, but they are nevertheless created beings, and God created them, as will be
explained below. In Bereshith Rabbah (on Gen. iii. 24) we read the following remark of our Sages: "The angel is called 'the flame of the sword which turned every way' (Gen. iii. 24), in accordance with the words, 'His ministers a flaming fire' (Ps. civ. 4); the attribute, 'which turned every way' is added, because angels are changeable in form they appear at one time as males, at another as females; now as spirits; now as angels." By this remark they clearly stated that angels are incorporeal, and have no permanent bodily form independent of the mind [of him who perceives them], they exist entirely in prophetic vision, and depend on the action of the imaginative power, as will be explained when speaking on the true meaning of prophecy. As to the words "at another time as females," which imply that the Prophets in prophetical vision perceived angels also in the form of women, they refer to the vision of Zechariah (v. 9), "And, behold, there came out two women, and the wind was in their wings." You know very well how difficult it is for men to form a notion of anything immaterial, and entirely devoid of corporeality, except after considerable training: it is especially difficult for those who do not distinguish between objects of the intellect and objects of the imagination, and depend mostly on the mere imaginative power. They believe that all imagined things exist or at least have the possibility of existing: but that which cannot be imagined does not exist, and cannot exist. For persons of this class--and the majority of thinkers belong to it--cannot arrive at the true solution of any question, or at the explanation of anything doubtful. On account of this difficulty the prophetic books contain expressions which, taken literally, imply that angels are corporeal, moving about, endowed with human form, receiving commands of God, obeying His word and performing whatever He wishes, according to His command. All this only serves to lead to the belief that angels exist, and are alive and perfect, in the same way as we have explained in reference to God. If the figurative representation of angels were limited to this, their true essence would be believed to be the same as the essence of God, since, in reference to the Creator expressions are likewise employed, which literally imply that He is corporeal, living, moving and endowed with human form. In order, therefore, to give to the mind of men the idea that the existence of angels is lower than the existence of God, certain forms of lower animals were introduced in the description of angels. It was thereby shown, that the existence of God is more perfect than that of angels, as much as man is more perfect than the lower animals. Nevertheless no organ of the brute creation was attributed to the angels except wings. Without wings the act of flying appears as impossible as that of walking without legs: for these two modes of motion can only be imagined in connection with these organs. The motion of flying has been chosen as a symbol to represent that angels possess life, because it is the most perfect and most sublime movement of the brute creation. Men consider this motion a perfection to such an extent that they themselves wish to be able to fly, in order to escape easily what is injurious, and to obtain quickly what is useful, though it be at a distance. For this reason this motion has been attributed to the angels.
There is besides another reason. The bird in its flight is sometimes visible, sometimes withdrawn from our sight; one moment near to us, and in the
next far off: and these are exactly the circumstances which we must associate with the idea of angels, as will be explained below. This imaginary perfection, the motion of flight, being the exclusive property of the brute creation, has never been attributed to God. You must not be misled by the passage, "And he rode upon a cherub, and he did fly" (Ps. xviii. 10), for it is the cherub that did fly, and the simile only serves to denote the rapid arrival of that which is referred to in that passage. Comp.: "Behold, the Lord rideth upon a swift cloud, and shall come into Egypt" (Isa. xix. 1); that is, the punishment alluded to will come down quickly upon Egypt. Nor should expressions like "the face of an ox," "the face of a lion," "the face of an eagle," "the sole of the foot of a calf," found in the prophecies of Ezekiel (i. 10 and 7) mislead you; for all these are explained in a different manner, as you will learn later, and besides, the prophet only describes the animals (ḥayyot). The subject will be explained (III. 1.), though by mere hints, as far as necessary, for directing your attention to the true interpretation.
The motion of flying, frequently mentioned in the Bible, necessitates, according to our imagination, the existence of wings: wings are therefore given to the angels as symbols expressive of their existence, not of their true essence. You must also bear in mind that whenever a thing moves very quickly, it is said to fly, as that term implies great velocity of motion. Comp. "As the eagle flieth" (Deut. xxviii. 49). The eagle flies and moves with greater velocity than any other bird, and therefore it is introduced in this simile. Furthermore, the wings are the organs [lit. causes] of flight; hence the number of the wings of angels in the prophetic vision corresponds to the number of the causes which set a thing in motion, but this does not belong to the theme of this chapter. (Comp. II. iv. and x.)