Explaining the import of “circles” as opposed to “lines” in the Ari’s depiction, Ramchal makes the following important remark in his comments to Petach 13 which will help us understand his discussion of overall providence as opposed to the detailed mode of governance.
He says that “the causal relationship between Sephirot  can be understood from the ‘circles’ (that were envisioned), while governance  can be understood from the ‘lines’ (that were envisioned)”.
That’s to say that what Ari’s depiction reveals is that God employs two different systems for interacting with the world through His Sephirot: one in which He interacts on a simple, overall cause-and-effect level of governance (i.e., if A happens then B will happen; just as Keter brings on Chochma, etc.); and another in which He interacts more dynamically and unpredictably in a detailed mode (i.e., if A happens then B may happen or it may not and L might happen; just as Chochma can affect Binah which is by its side, or Chessed which is beneath it, etc.) .
Ramchal expounds upon these two systems elsewhere at length. As he explains it in Da’at Tevunot (190), on one level, God maintains the world and keeps it moving onward toward its ultimate goal come-what-may and despite specific moral or immoral events in the world. Ramchal terms that mode God’s overall providence since it doesn’t touch on variables. On another level, though, God does indeed take specific moral or immoral events into consideration, and Ramchal terms that the detailed mode of governance since it takes every factor into account .
Understand that the latter can’t thwart God’s goals for the world; all they do is affect our own standing in the world, depending on our spiritual and ethical standing, but that’s besides the subject at hand. But this will be discussed in different junctures in this work.
This dynamism and interaction also explains Ramchal’s statement in Petach 10 (as well as in his comments there) to the effect that the Sephirot are interdependent,… sequential, and … sequestered within each other, as well as his discussion of Sephirot sometimes being “encased” in each other or seeming to “emerge” from another.
But there’s another point to be made here which is fundamentally important: Ari never said anything about two systems of interaction; that’s how Ramchal explains these “metaphors”. So let’s examine that next.
[1} This is termed hishtalshilut in Hebrew and it derives from the term for “lowering down” (shilshul) or acting as a “chain” (shalshelet). It thus refers to the descending and causative nature of the Sephirot from Keter to Chochma (etc.) downwards, and to the fixed nature of the relationship.
 This is termed hanhaga in Hebrew and it derives from the term for “to lead” “to drive” (nahag). And it thus refers to the dynamic nature of the Sephirot which interact from the top downward, as when Chochma leads to Chessed or when Binah leads to Gevurah (etc.), as well as from side to side, as when Chochma interacts with Binah or when Chessed interacts with Gevurah (etc.).
 As Ramchal worded it in Petach 10, a (vision of a) “circle” refers to a circular mode of governance without differentiation as to Chessed (Kindness), Din (Judgment) or Rachamim (Mercy), but rather as (i.e., it’s an expression of) overall providence…. And it is (a depiction of) the mystical notion of causality. The (vision of a) “straight line” on the other hand indicates a detailed mode of governance that is based on Chessed (Kindness), Din (Judgment) and Rachamim (Mercy, which are themselves laid out as) right, left or center (poles).
 Also see Petach 96 below; Klallim Rishonim 36; and Biurim Al Sefer Otzrot Chaim 14, 18.
(c) 2011 Rabbi Yaakov Feldman
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