וְעָבַר עָלָיו רוּחַ קִנְאָה וְקִנֵּא אֶת אִשְׁתּוֹ
But a spirit of jealousy had come upon him and he became jealous of his wife.
In many languages, there are two different terms to express the emotions of jealousy and envy. Envy consists of desiring what others have that you lack. Jealousy involves wanting to hold on to what you already have. In Hebrew, however, both terms have the same root. When Leah gave birth to several sons while Rachel remained barren, the Torah tells us וַתְּקַנֵא רָחֵל בַּאֲחֹתָהּ, and Rachel envied her sister (Gen. 30:1). In contrast, when Elijah was jealous for God’s honor, the prophet again uses the same root: קַנֹא קִנֵאתִי לַיהֹוָה, I have been jealous for the Lord (I Kings 19:9-10).
The word קִנְאָה with the meaning of envy is used in Tanach in a variety of contexts. But קִנְאָה as jealousy appears in the Torah only in two situations: in the relationship between God and man (קִֵל קַנָא, Ex. 20:5), and in this verse, which discusses the relationship between husband and wife. Idolatry begets קִנְאָה, and adultery begets קִנְאָה.
The commitment between husband and wife is very strong in Judaism—but it is not limitless. Had Judaism considered it an unlimited commitment, the institution of divorce as an instrument of separation could never have been recognized.
There is only one commitment that is absolute, ultimate and infinite: the commitment between man and God. God resents the attempt on the part of any finite being to share man with Him. He wants the whole of man. קֵל קַנָא; I, God, am intolerant of sharing. I want man for Myself; and not just a part of man, but the whole of man. (Rabbi Joseph B. Soloveitchik on Pesach, Sefirat ha-Omer and Shavu’ot, pp. 262-267)