Numbers 5:20
But if thou hast gone aside to another instead of thy husband, and if thou be defiled, and some man have lain with thee beside thine husband: But if thou hast gone aside to another instead of thy husband, and if thou be defiled, and some man have lain with thee beside thine husband:
The verse stands within the laws concerning jealousy in Numbers 5 and 6, which follow the numbering of the people and of Levi and the offices of the families of Levi in Numbers 1-4. It is part of the law of jealousy for a wife suspected of infidelity when there is no direct evidence, in which she was brought before the priest with a barley meal offering and made to drink bitter water. The barley offering was not to expiate sin but to expose it, for if she was guilty the water would bring dreadful consequences leading to death, while if innocent it would do her no harm. The rite shows that God would remove even the suspicion of impurity from Israel.
The chapter shows God's abhorrence of sin and warns people to shun its destructive course and fearful end. In verses 19-21 God instituted the judicial oath through Moses, to be administered by the priest who held rightful authority to administer it especially in a case of alleged criminality, showing that in Jewish courts an accused person was put under oath as a witness in his own case. This is collateral proof that the oath commanded in Deuteronomy 6:13 and Deuteronomy 10:20 is a judicial oath.