“To this correspond two statements of Isaac that refer to the hidden subject of the third person, past tense, which Hebrew does not mark by a specific termination. In his comment on Genesis 1, he says: “In every place [in the Scriptures] where you find simply bam’, ‘asa, ‘he created, he made,’ know that it [the subject] is above the pure thought.”
But in his commentary on Yesirah 1:1 he explains the hidden subject of the verb haqaq, as “that which thought cannot attain.” Since for Isaac (who knows nothing of a definition of the Will as the first emanated being) the mahshabah itself is the first sefirah, then that which it cannot attain would therefore be nothing other than ‘en-sof, which is itself transcendent and hidden in relation to thinking.
The pure thought would be the supreme creative sphere of being, while ‘en-sof, as the Unknowable, already existed before all thought. Quite possibly this was in fact Isaac’s opinion, and I find nothing in his own statements to contradict this supposition. The difficulty, however, lies in the fact that all his disciples, Ezra ben Solomon, Azriel, Jacob ben Shesheth, and above all his own nephew, Asher ben David, who was closest to him, identify the Unknowable, at times explicitly, at times implicitly, with the first sefirah.
The rules of simple logic would lead to the conclusion that Isaac is the common source of this identification. The divine Thought would then be that which cannot be attained by human thought, and Isaac would therefore employ the word mahshabah in different senses: in one context it would designate the Thought of God, but in the expression “that which cannot be attained by thought,” the reference would be to human thought.
However, in the fragment of his commentary on Genesis, he even speaks, as we saw, of that which is above the “pure Thought,” that is, above the divine Thought. I cannot resolve this difficulty without doing violence to the texts. The unknowable in God is identified by the Christian Neoplatonist, Scotus Erigena, with the Nothing from which all creation proceeds.”
Gershom Scholem, Origins of the Kabbalah, pp. 270-2.