The sotah – a woman suspected of adultery – is one of the most misunderstood mitzvos in the Torah. Many people envision a jealous husband flying into a rage and dragging his wife to the Temple, where the kohanim (priests) force water down her throat, potentially causing her to explode on the spot. As with so many things, the popular misconception is far removed from the truth. In reality, the husband had previously expressed to his wife his jealousy regarding a certain man. The wife chooses to ignore this and sequesters herself with the object of her husband’s jealousy, a fact that is reported back to him by witnesses. They travel to the Temple, where the woman has the choice to opt out of the sotah process, which is tantamount to pleading “no contest.” She can decline at any point until almost the end. (After the Name of God is blotted out in the water, she can no longer refuse.) If she is in fact guilty, her sentence might be suspended for a period of years.
The Torah tells us that if the woman goes through the process and is innocent, she will be rewarded by conceiving and having a child. If she is guilty, not only does the woman expire, so does the adulterer (Mishnah Sotah 5:1). The sotah process ceased to be effective and was discontinued when adultery became rampant; since the husbands were equally guilty, the process wouldn’t work for them, so the results would be unreliable (Mishnah Sotah 9:9).
The basis of this mitzvah is to remove suspicion and jealousy from a marriage. This is so important that it’s the only time that God Himself gets involved in the proceedings by punishing the woman if she’s guilty or rewarding her if she has been slandered.
This mitzvah only applies in Temple times, when there’s a Sanhedrin. (Since there is no sotah process today, a man should be sure not to create the situation that would necessitate it. Since it is unresolvable, it is halachically problematic.) It is the topic of the Talmudic tractate of Sotah, as well as Hilchos Sotah in the Mishneh Torah. This mitzvah is #223 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.