Where did the notion of a Tzimtzum originate? Many suggest it comes from a couple of renditions of the pre-cosmic condition as found in the Zohar (1:15a) and in Zohar Chadash (V’etchanan, Kav HaMiddah). The latter more easily lends itself to that suggestion; and in fact Ramchal himself cites it as a reference .
Some find a source for it in a parable in Ramak’s Pardes (4:9) . But already Nachmanides cited the notion in his opening remarks of his comments to Sefer Yetzirah in the 13th Century, and Shem Tov Ibn Shem Tov spoke of it in the 15th Century.
But the idea first presents itself in Shemot Rabbah to Exodus 25:10, where God was said to restrict and foreshorten (l’tzamtzaim) His presence to a small specific area of the Tabernacle .
It seems, though, that two other early sources allude to the need for a Tzimtzum before there could be a creation: the idea that “God yearned for a home among the lower beings” (Midrash Tanchuma, Naso 16) which He obviously could not have had, had He not allowed for the environment that the lower beings would need; and the idea that God appeared in various “guises” at different times — as a warrior at the Red Sea, a sage at the giving of the Torah, etc. — depending on the needs of the time and circumstances (see Rashi to Exodus 20:2), which suggests that that He needed to assume the “guise” of a non-presence before the universe was created.
That having been said, it’s nonetheless true that it was Ari alone who made Tzimtzum a major component of his explanation of things, and it’s his understanding of it that calls for explanation and analysis.
 See his comments to Petach 30 (beginning of section 2 there). But also see the 3rd comment in Ari’s Derech Emet to Kav HaMiddah, and Eitz Chaim p. 11d.
 See R’ M.Y. Veinshtock’s Shulchan HaMa’arachot b’Sitrei HaChochma (Vol. 1 p. 133).
 Gershom Scholem famously declared that Ari turned the Midrash’s image on its head, for while the latter spoke of God narrowing and focusing His Presence into only one area, Ari referred to Tzimtsum as a setting aside or moving away of God’s presence. But the truth of the matter is that both refer to the unexpected “plasticity” of God’s presence, if you will, which is the main point.
(c) 2011 Rabbi Yaakov Feldman
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