Again, it was he [Cordovero] who tried to interpret the various stages of emanation as stages of the divine mind. The problem of the relation of the substance of En-Sof to the “organism,” the “instruments” (kelim: i. e. vessels or bowls), through which it works and acts was one to which he returned again and again. The intrinsic conflict between the theistic and the pantheistic tendencies in the mystical theology of Kabbalism is nowhere brought out more clearly than in his thought, and his attempts to synthesize the contradiction not only dominated the speculative side of his thinking but also produced tentative solutions which are frequently as profound and audacious as they are problematical. His ideas on the subject are summed up in the formula—a century before Spinoza and Malebranche,—that “God is all reality, but not all reality is God.” En-Sof, according to him, can also be called thought (i. e. thought of the world) “insofar as everything that exists is contained in [Their] substance. [They] encompasses all existence, but not in the mode of its isolated existence below, but rather in the existence of the substance, for [They] and existing things are {in this mode} one, and neither separate nor multifarious, nor externally visible, but rather [Their] substance is present in [Their] Sefiroth, and [They Themself] is everything, and nothing exists outside [Them].
Gershom Scholem, Major Trends in Jewish Mysticism; Seventh Lecture: Isaac Luria and his School