במדבר פרק ה, יב
דַּבֵּר אֶל-בְנֵּי יִשְרָּאֵּל וְאָּמַּרְ תָּ אֲלֵּהֶם אִיש אִיש כִי-תִשְטֶה אִשְתוֹ וּמָּעֲלָּה בוֹ מָּעַּל :
מסכת ברכות דף סג/א אמר רבי יוחנן למה נסמכה פרשת סוטה לפרשת תרומות ומעשרות לומר לך כל שיש לו תרומות ומעשרות ואינו נותנן לכהן סוף נצרך לכהן על ידי אשתו
When one’s wife becomes a Sotah, the husband would now need a Cohen to conduct the proper procedures for the test of the waters of a Sotah, thus, indicates that one previous had an improper interaction with a Cohen. Why is one punished with evident misbehavior of one’s wife as a result of the person’s improper dealings with a Cohen? Such a person is evidently stingy and greedy which lead to withholding from the Cohen (for example, terumah), so he probably is stingy and withholds the desires of his wife, leading her to seek outlets elsewhere.
One can also answer according to the Gemara (Sotah 2a) that a person connects with a wife as fitting with one’s level. (Thus, the ethical type of wife is appropriate for the type of ethical behavior of the man)
According to this latter explanation, we can explain the Gemara there that states that Reish Lakeish begins teaching the Gemara Sotah with this saying that a person connects with a wife as fitting with the man’s level. The Gemara does not explain why he would begin specifically with this saying. Now we can understand that Reish Lakeish was bothered about the question above why a person who does not provide appropriately to the Cohen would lead to his wife sinning and now needing a Cohen. And, thus, the concept that a man receives a wife fitting to his level, begins the appropriate understanding of the events that surround a Sotah.
