Gnosticism is a name given to Christian sects by modern theologians who wanted to put the sects into categories. There were no ancient agnostics, only Christians. All you are saying is that the Jewish and Christian faiths are different.

As for the teaching of the Kabbalah, it very well could have been classified as a Jewish Gnostic faith. The Jewish faith did not have the idea of the "spark of life" or a "return to heaven" that the Christian Gnostics had; however, their teachings are still based on "secret knowledge." Salvation was not a Jewish idea.

"The Gnostics held that the material, empirical, human being is essentially an illusion that envelops, indeed imprisons, the inner, true self. It is only by acquiring knowledge or "memory" (in the Platonic sense of anamnesis) of this inner self that the Gnostic devotee can free himself from this hostile world and achieve ultimate spiritual fulfillment. While the Kabbalists held a similar view regarding the "sparks," their Jewish commitment to the world's essential goofiness led them to transform the sparks doctrine into a vehicle for world-redemption."..... "All of these ideas are found in relatively unaltered form in the Lurianic Kabbalah and in the writings of the Hasidim that are based on Luria's ideas. The existence of an inner divine self (Tzelem, image, or "Godly soul") in the Kabbalah, which acts as a forgotten "celestial counterpart" to a man's empirical ego, is common to both of these traditions, as is the idea of the necessary awakening of this inner self and its ultimate reunion with the infinite divine principle. This awakening occurs, according to the Kabbalists, only through a person's attaining a deep, abiding, emotional/spiritual knowledge of his true self, and is achievable only when an "arousal from above" compliments man's own "arousal from below."

http://www.newkabbalah.com/gnos.html

If a Christian sect was following the teachings of the Kabbalah they would have been classified as Gnostic. Kabbalistic thought is not really any different from Gnosticism. The word Gnosticism is applied to Christian faiths and not the Jewish faiths. http://www.newkabbalah.com/gnos.html

"GNOSTICISM:.
An esoteric system of theology and philosophy. It presents one of the most obscure and complicated problems in the general history of religion. It forced itself into prominence in the first centuries of the common era, and the Church Fathers were constrained to undertake its refutation. Writers on the history and dogmas of the Church have therefore always devoted much attention to the subject, endeavoring to fathom and define its nature and importance. It has proved even more attractive to the general historians of religion, and has resulted during the last quarter of a century in a voluminous literature, enumerated by Herzog-Hauck ("Real-Encyc." vi. 728). Its prominent characteristic being syncretism, the scholars, according to their various points of view, have sought its origin, some in Hellenism (Orphism), some in Babylonia, others elsewhere. This question, however, can not be discussed here, as this article deals with purely Jewish gnosticism.

Jewish Gnosticism.
Jewish gnosticism unquestionably antedates Christianity, for Biblical exegesis had already reached an age of five hundred years by the first century C.E. Judaism had been in close contact with Babylonian-Persian ideas for at least that length of time, and for nearly as long a period with Hellenistic ideas. Magic, also, which, as will be shown further on, was a not unimportant part of the doctrines and manifestations of gnosticism, largely occupied Jewish thinkers. There is, in general, no circle of ideas to which elements of gnosticism have been traced, and with which the Jews were not acquainted. It is a noteworthy fact that heads of gnostic schools and founders of gnostic systems are designated as Jews by the Church Fathers. Some derive all heresies, including those of gnosticism, from Judaism (Hegesippus in Eusebius, "Hist. Eccl." iv. 22; comp. Harnack, "Dogmengesch." 3d ed. i. 232, note 1). It must furthermore be noted that Hebrew words and names of God provide the skeleton for several gnostic systems. Christians or Jews converted from paganism would have used as the foundation of their systems terms borrowed from the Greek or Syrian translations of the Bible. This fact proves at least that the principal elements of gnosticism were derived from Jewish speculation, while it does not preclude the possibility of new wine having been poured into old bottles."

http://www.jewishencyclopedia.com/articles/6723-gnosticism

Pre-Christian.
"Cosmogonic-theological speculations, philosophemes on God and the world, constitute the substance of gnosis. They are based on the first sections of Genesis and Ezekiel, for which there are in Jewish speculation two well-established and therefore old terms: "Ma'aseh Bereshit" and "Ma'aseh Merkabah." Doubtless Ben Sira was thinking of these speculations when he uttered the warning: "Seek not things that are too hard for thee, and search not out things that are above thy strength. The things that have been commanded thee, think thereupon; for thou hast no need of the things that are secret" (Ecclus. [Sirach] iii. 21-22, R. V.). The terms here emphasized recur in the Talmud in the accounts of gnosis. "There is no doubt that a Jewish gnosticism existed before a Christian or a Judæo-Christian gnosticism. As may be seen even in the apocalypses, since the second century B.C. gnostic thought was bound up with Judaism, which had accepted Babylonian and Syrian doctrines; but the relation of this Jewish gnosticism to Christian gnosticism may, perhaps, no longer be explained "(Harnack," "Geschichte der Altchristlichen Litteratur," p. 144). The great age of Jewish gnosticism is further indicated by the authentic statement that Johanan b. Zakkai, who was born probably in the century before the common era, and was, according to Sukkah 28a, versed in that science, refers to an interdiction against "discussing the Creation before two pupils and the throne-chariot before one."

Kabbalistic Thought - IS GNOSTICISM. It is exactly what is meant my "gnosis." In the Christian faith. There is special knowledge that only the selected few can know about life, the universe, god, and salvation. Secret religious teaching is Gnosticism and the Kabbalah and its secrets is a kind of Jewish Gnosticism.