...are only in her when Yesod is with her... This is explained in many places in the Zohar and Tikkuney Zohar, and this is the mystery contained in the verse, “The advantage of land is in everything” (Ecclesiastes 5:8). This is the mystery of the moon, which in its intrinsic nature is a “glass that does not shine”, yet through the power of the sun, she shines and is seen to be beautiful, as it says, “beautiful as the moon” (Song of Songs 6:10).
Such is the nature of Judgment (Din) and all that comes from it. If it is mitigated, it is the source of all joy (for the recipients justly deserve their reward and there is no “bread of shame”). But if it is unmitigated, it is the source of all evil, which is not so in the case of Kindness (Chessed). Fire is also like this: if the heat is at the necessary level, it provides great satisfaction, but if it is too hot, it burns. So it is with wine: if one drinks in moderation, it is “the wine that brings joy”, but if one drinks to excess, it is the wine that intoxicates. This is the mystery of the Nukva. If she is mitigated and sweetened with kindly influences (חסדים, chassadim), she arouses every kind of joy and love. But if she is unmitigated, on the contrary, she causes every kind of sadness. Yesod’s mission is precisely to sweeten Malchut.