Guide for the Perplexed, by Moses Maimonides, Friedländer tr. [1904], at sacred-texts.com
THE meaning of the Scriptural passage, "Behold I will send an angel before thee," etc. (Exod. xxiii. 20), is identical with the parallel passage in Deuteronomy which God is represented to have addressed to Moses at the revelation on Mount Sinai, namely, "I will raise them up a prophet from among their brethren," etc. (Deut. xviii. 18). The words, "Beware of him, and obey his voice," etc., said in reference to the angel, prove [that this passage speaks of a prophet]. For there is no doubt that the commandment is given to the ordinary people, to whom angels do not appear with commandments and exhortations, and it is therefore unnecessary to tell them not to disobey him. The meaning of the passage quoted above is this: God informs the Israelites that He will raise up for them a prophet, to whom an angel will appear in order to speak to him, to command him, and to exhort him; he therefore cautions them not to rebel against this angel, whose word the prophet will communicate to them. Therefore it is expressly said in Deuteronomy, "Unto him ye shall hearken" (Deut. xviii. 15); "And it shall come to pass that whosoever shall not hearken unto my words which he shall speak in my name," etc. (ibid. 19). This is the explanation of the words, "for my name is in him" (Exod. xxiv. 22). The object of all this is to say to the Israelites, This great sight witnessed by you, the revelation on Mount Sinai, will not continue for ever, nor will it ever be repeated. Fire and cloud will not continually rest over the tabernacle, as they are resting now on it: but the towns will be conquered for you, peace will be secured for you in the land, and you will be informed of what you have to do, by an angel whom I will send to your prophets; he will thus teach you what to do, and what not to do. Here a principle is laid clown which I have constantly expounded, viz., that all prophets except Moses receive the prophecy through an angel. Note it.