[From Die Bucher der Bibel, by E.M. Lilien]
("Teller/Revealer”). While the term is frequently used to refer to an itinerant Jewish preacher, in Jewish esoteric traditions a maggid is an angelic teacher; a spirit guide. The maggid is related to the historically earlier phenomenon of the Sar ha-Torah and to other angels of revelation and dreams (particularly Gabriel), but there does seem to be a meaningful distinction: A maggid is often the genius, the hypostasis, or personification of some high attribute or non-personal supernal reality like the Torah, Shekhinah, Wisdom, or the Mishnah. Occasionally the maggid is described as a kind of angelic apparition, but in most accounts it appears in the form of pneumatic possession. Though there is considerable variation in maggid accounts, conventionally a maggid manifests itself within the person, triggering automatic writing and xenoglossia (Maggid Mesharim; Hesed l'Avraham). Take, for example, this description of what happened to Moses Luzzato:
There is a young man...he is a holy man, my master and teacher...Rabbi Moses Hayyim Luzzato. For these two and half years a maggid has been revealed to him, a holy and tremendous angel who reveals wondrous mysteries to him....This is what happens. The angel speaks out of his mouth, but we, his disciples, hear nothing. The angel begins to reveal to him great mysteries. 
In contrast to this "silent speech," Joseph Caro's maggid was quite vocal:
No sooner had we studied two tractates of the Mishnah then our Creator smote us so that we heard a voice speaking out of the mouth of the saint, may his light shine. It was a loud voice with letters clearly enunciated. All the companions heard the voice but where unable to understand what was said. It was an exceedingly pleasant voice, becoming increasingly strong. 
It should be noted that in other accounts, Caro's maggid was understandable to bystanders.
Joseph Taitazak experienced his maggid as automatic writing . The presence of the maggid is sometimes unsought and spontaneous, but is more usually associated with intensive text study combined with some mystical discipline and or/ritual . It is in some way analogous to the Greek notion of a muse, though the maggid is largely bereft of the aesthetic dimension associated with a muse.
By the time of Chayyim Vital, the phenomenon was common enough that his teacher Isaac Luria had to spell out some criteria for distinguishing a legitimate maggid from a charlatan or mentally disordered person:
My master the Ari [Isaac Luria] gave a sign [through which one can recognize a reliable maggid]. It must constantly speak the truth, motivate one to do good deeds, and not err in a single prediction. If it can explain the secrets and mysteries of the Torah, it is certainly reliable. From its words, one can recognize its level. The mystery of ruach ha-kodesh [divine inspiration] is this: It is a voice sent from on high to speak to a prophet or to one worthy of ruach ha-kodesh. But such a voice is purely spiritual, and such a voice cannot enter the prophet's ear until it clothes itself in a physical voice. The physical voice in which it clothes itself is the voice of the prophet himself, when he is involved in prayer or Torah study. This voice clothes itself in his voice and is attached to it. It then enters the prophet's ear so that he can hear it. Without the physical voice of the individual himself, this could not possibly take place. Zal g'mor /Go forth and learn
- read more in the Encyclopedia of Jewish Myth, Magic, and Mysticism:http://www.amazon.com/Encyclopedia-Jewish-Myth-Magic-Mysticism/dp/0738709050
1. Louis Jacobs, Jewish Mystical Testimonies, pp. 171-172
2. Ibid., p. 124
3. Joseph Dan, The Heart and the Fountain, p. 177 - 179
4. Lawrence Fine, Physician of the Soul, Healer of the Cosmos, pp. 69-71; Dan, pp. 178-180
5. Aryeh Kaplan, Kabbalah and Meditation, pp. 223-224