Here’s the wording in the Petach again: While “The Crystalline Dew” presents all of the colors together, just as crystals do when light strikes them, Radlah presents itself otherwise: as one thing in one instance and then immediately afterwards as its opposite.
This statement comes to differentiate Radlah from Erich Anpin, the next Partzuf down, as we’d indicated. For, Ari in fact locates The Crystalline Dew within one of the highest reaches of Erich Anpin . The point of the matter is that while all of the lights in Erich Anpin illuminate distinctly and clearly, that’s not the case with the lights of Radlah — they reveal a light as this at one point and as that at another, as we’d seen.
The simple explanation is that the higher up one goes in the chain of revelation, the hazier and more inscrutable the distinctions between the parts, and the lower down on goes, the clearer they are. So while those in Radlah aren’t the most arcane and can be distinguished to some degree, though in confounding ways, they’re nonetheless less clear and distinct than the lights below them in Erich Anpin and downward.
Here’s how Ramchal goes on to underscore the confounding nature of Radlah‘s lights in the rest of the Petach. In fact, he says, though it stays in this transformative state in which an instances of ”yes” and one of “no” i.e., one thing and its opposite, appear at the same time, we simply can’t grasp how both a “yes” and the “no” could exist at the same time. That is, we simply can’t understand how it seems to be an instance of “yes” and then immediately afterwards it seems not to be that at all.
 See Eitz Chaim, Sha’ar haClallim 2 and Pri Eitz Chaim, Sha’ar Selichot 8.
(c) 2015 Rabbi Yaakov Feldman
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