NOTES for Num 5:1-31
The test prescribed by the Book of Numbers for the fidelity of a wife whose husband had come to doubt her faithfulness recalls very ancient times, far more ancient than the age of Moses and the Exodus. This is deep archaism, pre-Yahwistic, pre-biblical. Why, one might ask, preserve such old customs, and even record them as law? The simplest answer is that the Torah quite often preserves ancient norms of customary law - as a concession to those who cannot imagine relationships between people in any other way. Of course, it does so with limitations - just as, for example, the Torah limits a person's right to avenge an offense or damage, demanding from the avenger proportionality in the damage he inflicts on the offender.
It is the same with jealousy: in ancient societies adultery was treated with utmost severity. The usual punishment for it was death, and as a rule it came at the hand of the husband who had been betrayed. Here, however, in the Book of Numbers, a distinctive procedure is proposed for testing marital fidelity - by the mutual consent of the two. Precisely mutual consent: refusal was possible, but then all the husband's suspicions would have remained in force, and God alone knows what they might eventually have led to. Such a test was in any case the lesser of two evils, if the wife passed through it successfully.
Of course, there was nothing good in such tests. This is precisely a concession to human sinfulness, one of whose manifestations is jealousy, especially groundless jealousy. There was also something else here: the desire to reconcile spouses whose marriage was already close to falling apart. The test was serious enough, and the procedure awaiting the wife suspected of infidelity was far from pleasant. If everything ended well, then in the husband, if he had even a drop of love left for his wife, a certain immunity would inevitably have to develop both against such tests and against jealousy.
Of course, this immunity could not be especially strong, because in this case it was not a matter of recognizing one's own jealousy as a spiritual problem, but rather of a kind of psychological shock that could and should be remembered. Still, that was better than nothing. The root of the problem remained, but at least its consequences could be softened. Spiritual work, however, presupposed something entirely different - but that is another story.