Says the Kuzari [4/5]:
וְאַל תַּאֲמִין לַמִּתְחַכֵּם, שֶּׁיּאמַר כִּי מַחֲשַׁבְתּו מִתְחַבֶּרֶת עַל סֵדֶר עַד שֶׁיַּגִּיעַ אֶל כָּל הָעִנְיָנִים הַצְּרִיכִים בָּאֱלהוּת בְּשִׂכְלו בִּלְבַד מִבִּלְתִּי שֶׁיִּסְמךְ אֶל מֻרְגָּשׁ, בִּרְאות דִּמְיון מִמִּלּות או מִכְּתָב או מִצּוּרות נִרְאות או מִתְדַּמּות. הֲלא תִרְאֶה שֶׁאֵינְךָ יָכול לִכְלל כָּל עִנְיָנֵי תְפִלָּתְךָ בַּמַּחֲשָׁבָה לְבַדָּהּ בִּלְתִּי קְרִיאָה, וְלא תוּכַל לִסְפּר עַד מֵאָה, דֶּרֶךְ מָשָׁל, בַּמַּחֲשָׁבָה לְבַדָּהּ בְּלא דִּבּוּר, כָּל שֶׁכֵּן אִם תִּהְיֶה הַמֵּאָה מִמִּנְיָנִים מִתְחַלְּפִים, וְלוּלֵא הַהֶרְגֵּשׁ שֶׁהוּא כולֵל הַסֵּדֶר הַהוּא הַשִּׂכְלִי בְּדִמְיונות וּתְנוּעות, לא הָיָה נִכְלָל. וְכֵן מִסְתַּדֶּרֶת לַנָּבִיא גְּדֻלַּת הָאֱלהִים וִיכָלְתּו וְרַחֲמָנוּתו וְחָכְמָתו וְחַיּוּתו וּתְמִידוּתו וּמַלְכוּתו, וְשֶׁאֵינֶנּוּ צָרִיךְ לַכּל וְשֶׁהַכּל צְרִיכִים לו, וּמַעֲלָתו הַמְיֻחֶדֶת וּקְדֻשָּׁתו, בְּמַה שֶּׁהוּא רואֶה פִתְאום בְּרֶגַע אֶחָד מִגְּדֻלַּת הַצּוּרָה הַהִיא הַנִּבְרֵאת לו וְהודָהּ וַהֲדָרָהּ, וְהַתְּכוּנות וְהַכֵּלִים הַמּורִים עַל הַיְכלֶת, כַּיָּד הַנְּטוּיָה וְהַחֶרֶב הַשְּׁלוּפָה וְהָאֵשׁ וְהָרוּחַ וְהַבְּרָקִים וְהָרְעָמִים הַמְשַׁמְּשִׁים בְּמַאֲמָרו, וְהַדִּבּוּר הַיּוצֵא מִבֵּינֵיהֶם בְּאַזְהָרות וּבְהודָעַת מַה שֶּׁהָיָה וְיִהְיֶה, וּמַעֲמַד בְּנֵי אָדָם, וְהַמַּלְאָכִים לְפָנָיו נִכְנָעִים, וִיצִיאַת כָּל צָרְכֵיהֶם מֵאִתּו, יַסְפִּיק לָהֶם וְלא יֶחְסַר מְאוּמָה, יַגְבִּיהַּ הַשָּׁפָל וְיַשְׁפִּיל הַגָּבהַּ, וְיִפְשׁט יְמִינו לַשָּׁבִים וְיִקְרָא אֲלֵיהֶם: מִי-יודֵעַ יָשׁוּב וְנִחַם הָאֱלהִים (יונה ג), וְיֶאֱנַף וְיִכְעַס עַל הָרְשָׁעִים, מְהַעְדֵּה מַלְכִין וּמְהָקִים מַלְכִין, וּלְפָנָיו אֶלֶף אַלְפִין יְשַׁמְּשׁוּנֵהּ וְגו' (דניאל ז,י), כָּל זֶה וְהַדּומֶה לָזֶה יִרְאֶה הַנָּבִיא בְּרֶגַע אֶחָד, וְיִכָּנֵס הַמּורָא וְהָאַהֲבָה תְּקוּעִים בְּנַפְשׁו כָּל יְמֵי חַיָּיו, וְהולֵךְ כָּל יְמֵי חַיָּיו חושֵׁק, הומֶה וּמְבַקֵּשׁ שֶׁיִּתְרָאֶה אֵלָיו פַּעַם שְׁנִיָּה או שְׁלִישִׁית. וּכְבָר נֶחְשַׁב לִשְׁלמה לְדָבָר גָּדול הַשְׁתֵּי פְעָמִים, בְּאָמְרו: ,הַנִּרְאֶה אֵלָיו פַּעֲמָיִם' (מלכים א, א). מָתַי הִגִּיעַ הַפִּילוסוף עַל כָּזֶה בִּתְבוּנָתו?
Do not believe him who considers himself wise in thinking that he is so far advanced that he is able to grasp all metaphysical problems with the abstract intellect alone, without the support of anything that can be conceived or seen, such as words, writing, or any visible or imaginary forms. Can't you see that you aren't able even to collect the burden of your prayer in thought alone, without reciting it? Neither can you reckon up to a hundred without speaking, still less if this hundred be composed of different numbers. Were it not for the sensible perception which encompasses the organization of the intellect by means of similar sayings, that organization could not be maintained. In this way, prophets’ images picture God's greatness, power, loving kindness, omniscience, life, eternity, government, and independence, the dependence of everything on Him, His unity, and holiness, and in one sudden flash stands revealed this grand and majestic figure with its splendour, its characteristics, the instruments which typify power, etc., the up-lifted hand, the unsheathed sword, fire, wind, thunder and lightning which obey his behest, the word which goes forth to warn, to announce what has happened, and to predict. Many angels stand humbly before Him, and He gives them according to their requirements without stint. He raises the lowly, humbles the mighty, and holds out His hand to the repentant, saying to them: 'Who is conscious [of a sin] shall repent' (Jonah iii. 9). He is wroth with the wicked, deposes and appoints, whilst before Him 'thousand thousands minister unto Him' (Dan. vii. 10). Such are the visions which the prophet sees in one second. Thus fear and love come to him naturally, and remain in his heart for the whole of his life. He even yearns and longs to behold the vision again and again. Such a repetition was considered a great event for Solomon, in the words: 'The Lord who has appeared to him twice' (1 Kings xi. 9). Will a philosopher ever achieve the same result?
So prophecy is a vision that comes suddenly and does not require the usual processing that intellectual enterprises would require such as deduction, induction or analysis. He just sees it with a prophetic eye and "gets it".
The Rambam [Yesodei Hatorah 7/2-3] describes a similar experience:
ב. הנביאים מעלות מעלות הן כמו שיש בחכמה חכם גדול מחבירו כך בנבואה נביא גדול מנביא וכולן אין רואין מראה הנבואה אלא בחלום בחזיון לילה או ביום אחר שתפול עליהן תרדמה כמו שנאמר במראה אליו אתודע בחלום אדבר בו וכולן כשמתנבאים אבריהן מזדעזעין וכח הגוף כשל ועשתנותיהם מתטרפות ותשאר הדעת פנויה להבין מה שתראה כמו שנאמר באברהם והנה אימה חשכה גדולה נופלת עליו וכמו שנאמר בדניאל והודי נהפך עלי למשחית ולא עצרתי כח:
ג. הדברים שמודיעים לנביא במראה הנבואה דרך משל מודיעין לו ומיד יחקק בלבו פתרון המשל במראה הנבואה וידע מה הוא כמו הסולם שראה יעקב אבינו ומלאכים עולים ויורדים בו והוא היה משל למלכיות ושעבודן וכמו החיות שראה יחזקאל והסיר נפוח ומקל שקד שראה ירמיה והמגלה שראה יחזקאל והאיפה שראה זכריה וכן שאר הנביאים מהם אומרים המשל ופתרונו כמו אלו ויש שהן אומרים הפתרון בלבד ופעמים אומרים המשל בלבד בלא פתרון כמקצת דברי יחזקאל וזכריה וכולן במשל ודרך חידה הם מתנבאים:
2. There are a number of levels among the prophets. Just as with regard to wisdom, one sage is greater than his colleague, so, too, with regard to prophecy, one prophet is greater than another. They all, [however, share certain commonalities]. They receive prophetic visions only in a visionary dream or during the day after slumber has overtaken them, as [Numbers 12:6] states: "I make Myself known to him in a vision. I speak to him in a dream."
When any of them prophesy, their limbs tremble, their physical powers become weak, they lose control of their senses, and thus, their minds are free to comprehend what they see, as [Genesis 15:12] states concerning Abraham: "and a great, dark dread fell over him." Similarly, Daniel [10:8] states: "My appearance was horribly changed and I retained no strength."
3. When a prophet is informed of a message in a vision, it is granted to him in metaphoric imagery. Immediately, the interpretation of the imagery is imprinted upon his heart, and he knows its meaning.
For example, the ladder with the angels ascending and descending envisioned by the patriarch, Jacob, was an allegory for the empires and their subjugation [of his descendants]. Similarly, the creatures Ezekiel saw, the boiling pot and the rod from an almond tree envisioned by Jeremiah, the scroll Ezekiel saw, and the measure seen by Zechariah[were all metaphoric images]. This is also true with regard to the other prophets.
Some would relate the allegory and its explanation as these did. Others would relate only the explanation. At times, they would relate only the imagery without explaining it, as can be seen in some of the prophecies of Ezekiel and Zechariah.
All of the prophecies come in the form of metaphoric imagery and allegories.
But the Rambam also writes something different [Moreh 26]:
PROPHECY is, in truth and reality, an emanation sent forth by the Divine Being through the medium of the Active Intellect, in the first instance to man's rational faculty, and then to his imaginative faculty; it is the highest degree and greatest perfection man can attain: it consists in the most Perfect development of the imaginative faculty. Prophecy is a faculty that cannot in any way be found in a person, or acquired by man, through a culture of his mental and moral faculties: for even if these latter were as good and perfect as possible, they would be of no avail, unless they were combined with the highest natural excellence of the imaginative faculty.
It starts with the intellect and then goes to the imaginative faculty. The Rambam continues and lays down the prerequisites for receiving prophecy:
After these introductory remarks you will understand that a person must satisfy the following conditions before he can become a prophet: The substance of the brain must from the very beginning be in the most perfect condition as regards purity of matter, composition of its different parts, size and position: no part of his body must suffer from ill-health; he must in addition have studied and acquired wisdom, so that his rational faculty passes from a state of potentiality to that of actuality; his intellect must be as developed and perfect as human intellect can be; his passions pure and equally balanced; all his desires must aim at obtaining a knowledge of the hidden laws and causes that are in force in the Universe; his thoughts must be engaged in lofty matters: his attention directed to the knowledge of God, the consideration of His works, and of that which he must believe in this respect. There must be an absence of the lower desires and appetites, of the seeking after pleasure in eating, drinking, and cohabitation: and, in short, every pleasure connected with the sense of touch. (Aristotle correctly says that this sense is a disgrace to us, since we possess it only in virtue of our being animals; and it does not include any specifically human element, whilst enjoyments connected with other senses, as smell, hearing, and sight, though likewise of a material nature, may sometimes include [intellectual] pleasure, appealing to man as man, according to Aristotle. This remark, although forming no part of our subject, is not superfluous, for the thoughts of the most renowned wise men are to a great extent affected by the pleasures of this sense, and filled with a desire for them. And yet people are surprised that these scholars do not prophesy, if prophesying be nothing but a certain degree in the natural development of man.) It is further necessary to suppress every thought or desire for unreal power and dominion; that is to say, for victory, increase of followers, acquisition of honour, and service from the people without any ulterior object. On the contrary, the multitude must be considered according to their true worth; some of them are undoubtedly like domesticated cattle, and others like wild beasts, and these only engage the mind of the perfect and distinguished man in so far as he desires to guard himself from injury, in case of contact with them, and to derive some benefit from them when necessary. A man who satisfies these conditions, whilst his fully developed imagination is in action, influenced by the Active Intellect according to his mental training, -- such a person will undoubtedly perceive nothing but things very extraordinary and divine, and see nothing but God and His angels. His knowledge will only include that which is real knowledge, and his thought will only he directed to such general principles as would tend to improve the social relations between man and man.