The word Merkaba or Merkava (etymology Hebrew: "chariot", derived from the ancient Hebrew consonantal root r-k-b with general meaning "to ride (an animal, in a chariot)") is used in the Bible (Ezekiel 1:4-26) to refer to the throne-chariot of God, the four-wheeled vehicle driven by four Cherubim, each of which has four wings and four faces (of a man, lion, ox, and eagle). In medieval Judaism, the beginning of the book of Ezekiel was regarded as the most mystical passage in the Bible, and its study was discouraged, except by mature individuals with an extensive grounding in the study of traditional Jewish texts.
The earliest merkabah speculations were exegetical expositions of the prophetic
visions of God in the heavens, and the divine retinue of angels, hosts, and
heavenly creatures surrounding God. The earliest evidence suggests that merkabah
homiletics did not give rise to ascent experiences - as one rabbinic sage
states: "Many have expounded upon the merkabah without ever seeing it" (Tosefta'
Megillah 3[4]:28).
The Talmudic interdictions concerning merkabah speculation are numerous and
widely held. Discussions concerning the merkabah were limited to only the most
worthy sages, and admonitory legends are preserved about the dangers of
overzealous speculation concerning the merkabah. The sages Rabbi Yochanan Ben
Zakkai (d. ca. 80 CE) and later, Rabbi Akiva (d. 135) were deeply involved in
merkabah speculation. Rabbi Akiva and his contemporary Rabbi Ishmael ben Elisha
are most often the protagonists of later merkabah ascent literature.
Beyond the rabbinic community, Jewish apocalyptists also engaged in visionary
speculations concerning the divine realm and the divine creatures which are
remarkably similar to the rabbinic material. A small number of texts unearthed
at Qumran indicate that the Dead Sea community also engaged in merkabah
speculation. Recently uncovered Jewish mystical texts also evidence a deep
affinity with the rabbinic merkabah homilies. Recently, considerable scholarly
attention has been paid to the use of merkabah themes in early Jewish-Christian
circles.
The merkabah homilies eventually consisted of detailed descriptions of multiple
layered heavens (usually seven in number), often guarded over by angels, and
encircled by flames and lightning. The highest heaven contains seven palaces
(hekhalot), and in the innermost palace resides a supreme divine image (God's
Glory or an angelic image) seated on a throne, surrounded by awesome hosts who
sing God's praise.
The ascent texts are extant in four principal works, all redacted well after the
third but certainly before the ninth century CE. They are: 1) Hekhalot Zutartey
("The Lesser Palaces"), which details an ascent of Rabbi Akiva; 2) Hekhalot
Rabbati ("The Greater Palaces"), which details an ascent of Rabbi Ishmael; 3)
Ma`aseh Merkabah ("Account of the Chariot"), a collection of hymns recited by
the "descenders" and heard during their ascent; and 4) Sepher Hekhalot ("Book of
Palaces," also known as 3 Enoch), which recounts an ascent and divine
transformation of the biblical figure Enoch into the archangel
Metatron, as
related by Rabbi Ishmael.
A fifth work provides a detailed description of the Creator as seen by the
"descenders" at the climax of their ascent. This work, preserved in various
forms, is called Shi`ur Qomah ("Measurement of the Body"), and is rooted in a
mystical exegesis of the Song of Songs, a book reputedly venerated by Rabbi
Akiva. The literal message of the work was repulsive to those who maintained
God's incorporeality; Maimonides (d. 1204) wrote that the book should be erased
and all mention of its existence deleted.
While throughout the era of merkabah mysticism the problem of creation was not
of paramount importance, the treatise Sefer Yetzirah ("Book of Creation")
represents an attempt at cosmogony from within a merkabah milieu. This text was
probably composed during the seventh century CE, and evidences influence of
Neoplatonism, Pythagoreanism, and Stoicism. It features a linguistic theory of
creation in which God creates the universe by combining the 22 letters of the
Hebrew alphabet, along with emanations represented by the ten numerals, or
sefirot.
http://en.wikipedia.org/wiki/Merkabah