Is Kabbalah looked down upon by “serious” Jewish practitioners?
It depends upon what you mean by “serious.” If you mean rationalistic and philosophical, the answer is yes: some do. If you mean deeply observant, the answer can be yes or no. Nobody is more observant than Hasidic Jews and their religious culture is steeped in mysticism; other Orthodox Jews abhor mysticism. It’s interesting to note how much of Kabbalah has worked its way into mainstream Jewish observance-when Jews greet the Sabbath, for example, they are following a custom that began among the mystics in Safed, Palestine in the 1500s.
