Numbers 5:19
And the priest shall charge her by an oath, and say unto the woman, If no man have lain with thee, and if thou hast not gone aside to uncleanness with another instead of thy husband, be thou free from this bitter water that causeth the curse:
The verse belongs to the laws concerning jealousy in Numbers 5 and 6, which stand among other instructions including the laws concerning the Nazarites and closing with the blessing the priests were to place upon the children of Israel. The oath in the verse is a judicial oath instituted through Moses, administered by the priest in a case of alleged criminality where a woman accused of adultery is placed under oath as a witness in her own case. This shows that the oath commanded in Deuteronomy 6:13 and 10:20 was judicial.
The rite applied when a husband suspected infidelity without witnesses, whereas proved violation of the seventh commandment brought death. It used bitter water with a meal offering of a tenth of an ephah of barley meal with no oil or frankincense, an offering of jealousy and memorial bringing iniquity to remembrance. That offering was not an expiation for sin but a discoverer of sin.
In the verse the priest declares that if the woman has been faithful she will be free from the water's curse. If innocent the bitter water does her no harm and she is free, but if guilty it produces a condition leading to speedy and dreadful death, by which God rid Israel even of the suspicion of impurity. The chapter shows God's abhorrence of sin and warns people to shun its destructive course and fearful end. As a type it teaches that sin is not only the overt act but an inward condition of heart and character, needing confession for forgiveness and cleansing from all unrighteousness.