Likutei Moharan, Part II 32:4/ליקוטי מוהר"ן·תנינא ל״ב:ד׳

14. And know! there is a lower unification in this world which is carried out with such great virtue, sanctity and purity that the upper unification is dependent upon it. The couple, i.e., the man and the woman, are so virtuous—she is very virtuous and without a shred of spiritual deficiency, and he too is very virtuous—and their coupling is with such virtue and sanctity that the upper unification is dependent upon it. This is because: If iYsh (a man) and ishaH (a woman) are worthy, the Divine Presence resides in their midst (Sotah 17a). He contains a Yod, and she contains a Heh. These are [the letters of] the upper rectification. This particular coupling and lower unification is extremely valuable, since in this world a lower unification is carried out with such great sanctity that the upper unification is dependent upon it.

2Now see, the spirit of jealousy, i.e., the concept of the spirit of Mashiach, which zealously protests immorality—what relevance does it have here being that they are very holy and pure? But know! here, the spirit of jealousy is for the sake of love. For it is brought in the Zohar (I, 245a) : Love unaccompanied by jealousy is not true love. This is as it is written: “for love is as fierce as death, jealousy as hard as the grave” (Song of Songs 8:6). For jealousy is an indication of love. On account of his great love he protests zealously concerning her. “Do not seclude yourself” so that the love will not be ruined, God forbid. This is what the aforementioned spirit of jealousy accomplishes here for the love.

3However, because the lower unification is nonetheless in this world, the spirit of jealousy has the power to ruin their marital harmony, God forbid. Although the jealousy is for the sake of love, it has the power to instigate strife as a result of his jealousy for her.