As Ramchal explains in his comments here, this is a depiction of the descent sequence (השתלשלות), “whereby each light is emanated by and emerges from another light” gradually and step by step. And it comes about through the process of zivvug — “conjunction”, “union”, or intercourse in human terms.
As he words it in the Petach itself, of these two producing lights, one would be “male” and from the side of MaH, and one “female” and from the side of BaN. They would then produce the light that needs to be produced by their conjunction, which will thus be constructed out of both MaH and BaN.
That’s to say that everything — even supernal lights, as in this instance — was designed to be produced by the union of “male” (MaH in this instance) and “female” (BaN here) much the way that children are born by the union of a mother (an Imma in Hebrew) and a father (Abba).
Ramchal tempers the sexual implications by offering in his comments to the Petach that this works the way ideas are “born” too, in that they’re produced by the rapid interaction of other, preceding thoughts. But his central point here is that natural and supernatural entities are produced by the rapid (i.e., excited) interaction and union of male and female progenitors .
As Ar”i stated the principle, “the zivvug of Abba and Imma comes about so as to have lights from yet higher levels descend onto lower levels …. And the intention behind the zivvug of Zeir Anpin and Nukveh was to have souls descend into this world” as in childbirth (Sha’ar HaKavvanot, K’riat Sh’ma 2) .
 See Eitz Chaim 39 on this analogy.
 The frankly sexual nature of the discussion is what flabbergasted non-Kabbalists when Kabbalah was first being discussed openly in Torah circles, and it’s probably what lay behind the edict that one shouldn’t study it before being married (or before 40 years of age, when one’s passions were presumably tempered and could read these things with more aplomb).
(c) 2013 Rabbi Yaakov Feldman
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