Guide for the Perplexed, by Moses Maimonides, Friedländer tr. [1904], at sacred-texts.com
PROPHECY is given either in a vision or in a dream, as we have said so many times, and we will not constantly repeat it. We say now that when a prophet is inspired with a prophecy he may see an allegory, as we have shown frequently, or he may in a prophetic vision perceive that God speaks to him, as is said in Isaiah (vi. 8), "And I heard the voice of the Lord saying, Whom shall I send, and who will go for us?" or he hears an angel addressing him, and sees him also. This is very frequent, e.g., "And the angel of God spake unto me," etc. (Gen. xxxi. 11); "And the angel that talked with me answered and said unto me, Dost thou not know what these are" (Zech. iv. 5); "And I heard one holy speaking" (Dan. viii. 13). Instances of this are innumerable. The prophet sometimes sees a man that speaks to him. Comp., "And behold there was a man, whose appearance was like the appearance of brass, and the man said to me," etc. (Ezek. xl. 3, 4), although the passage begins, "The hand of the Lord was upon me" (ibid. ver. 1). In some cases the prophet sees no figure at all, only hears in the prophetic vision the words addressed to him; e.g., "And I heard the voice of a man between the banks of Uali" (Dan. viii. 16); "There was silence, and I heard a voice" (in the speech of Eliphaz, Job iv. 16); "And I heard a voice of one that spake to me" (Ezek. i. 28). The being which Ezekiel perceived in the prophetic vision was not the same that addressed him: for at the conclusion of the strange and extraordinary scene which Ezekiel describes expressly as having been perceived by him, the object and form of the prophecy is introduced by the words, "And I heard a voice of a man that spake to me." After this remark on the different kinds of prophecy, as suggested by Scripture, I say that the prophet may perceive that which he hears with the greatest possible intensity, just as a person may hear thunder in his dream, or perceive a storm or an earthquake; such dreams are frequent. The prophet may also hear the prophecy in ordinary common speech, without anything unusual. Take, e.g., the account of the prophet Samuel. When he was called in a prophetic vision, he believed that the priest Eli called him; and this happened three times consecutively. The text then explains the cause of it, saying that Samuel naturally believed that Eli had called him, because at that time he did not yet know that God addressed the prophet in this form, nor had that secret as yet been revealed to him. Comp., "And Samuel did not yet know the Lord, and the word of the Lord was not yet revealed to him," i.e., he did not yet know, and it had not yet been revealed to him, that the word of God is communicated in this way. The words, "He did not yet know the Lord," may perhaps mean that Samuel had not yet received any prophecy; for in reference to a prophet's receiving divine communication it is said, "I make myself known to him in a vision, I speak to him in a dream" (Num. xii. 6). The meaning of the verse accordingly is this, Samuel had not yet received any prophecy, and therefore did not know that this was the form of prophecy. Note it.