Introducing the sotah-woman, a unique Torah status that isn't in play in the absence of the Temple. From the verses to the rabbinic focus on witnesses to what appears to be unfaithful behavior on the wife's part as accused by the husband. Plus, the connection between a Nazir and a sotah, and the order of the tractates. Also, the way the husband gets the process underway. Plus the debate over whether a person gets the spouse he (or presumably she) deserves, based on personal conduct, or whether the match is made before the couple is even born, with destiny (or Divine Providence) trumping any actions on the part of the people.