It could be objected that in the teachings of the ARI of blessed memory we seem to find the opposite – that the coupling which produces the Mental Powers is not continuous, while the coupling that channels vitality to the worlds is continuous (see Etz Chayim, Shaar HaZivugim ch. 1).
The answer is that here we are talking about qualities possessed by the Partzufim that enable them to function properly in the governmental order rather than about the actual functioning of the Partzufim. For the lights descend level by level in the chain of development as required by the governmental order. The Mental Powers contained in Zeir Anpin are the foundation of the overall governmental order of Justice based on Kindness-Judgment-Mercy. All the rest of the Partzuf of Zeir Anpin – Chessed-Gevurah-Tiferet and Netzach-Hod-Yesod – follows accordingly, but the essential root is the Mental Powers. Understand that we are now talking not about the functioning but rather about the nature of the lights on various levels – i.e. about the role of each light in the governmental order, not how it actually executes that role or function.