Despite some of the basic similarities (such as heavenly ascent) between Gnosticism and Hekhalot and Merkavah mysticism, there are also serious differences, such as the way that they understand the Hebrew Bible (Gnosticism denigrated it, while Hekhalot and Merkavah mystics held it in high regard). Deutsch points out that when Gnostic texts are analyzed and compared to Hekhalot and Merkavah texts, it is only a few of the Gnostic texts that really seem to have parallels to those in the Hekhalot and Merkavah corpus. And, those texts that do look related may be related because they were influenced by the Hekhalot and Merkavah texts, not the other way around.
How, then, are we to understand the relationship between Gnosticism and Hekhalot and Merkavah mysticism? Deutsch proposes that the best way to study these texts is to look at them from a comparative standpoint of how each group approached the sacred. It is only then that the similarities and differences will be revealed to a greater extent because, as Deutsch puts it, "only a framework can be constructed on the foundation of the available evidence." (p. 150)
Once someone reads a book like Joseph Dan's _The Ancient Jewish Mysticism_, I would recommend a book like this, which provides a detailed analysis of some of the debates within the field of Hekhalot and Merkavah mysticism. Deutsch pays attention to detail and argues his points persuasively. In the end, the evidence for Hekhalot and Merkavah mysticism being Jewish Gnosticism looks weak. But, although there was probably no unified Rabbinic Gnosticism, there probably were some Gnostic rabbis who helped to shape the movement that produced the Hekhalot and Merkavah mystical texts.