"Why does the subject of the suspected adulteress [the Sotah] immediately follow the laws of offerings and tithes for the kohanim?
This comes to teach us that whoever does not hand over his tithes to the Kohen will in the end require the Kohen's services to deal with his wife." (Berachot 63a)
What is the connection between giving terumot and maaserot (tithes) and the Sotah?
The Professor and the Villagers
There was once a brilliant professor. The man was fluent in a dozen languages; he held doctorates in several sciences, including physics, biology, and chemistry. Everywhere he went, people honored him for his erudition and brilliance.
Once the professor found himself in a sleepy backwater, a small town populated by simple farmers and tradesmen. The townspeople questioned him as to his profession, and the professor replied that he was a medical doctor.
When one of his friends heard about this incident, he was surprised. "With all of your academic degrees and brilliance - why did you tell them that you're a general practitioner?"
"Why, it was the obvious thing to do," explained the professor. "These simple villagers have neither need nor appreciation for my knowledge of botany and physics and all the other subjects which I have studied in great depth. However, they have great respect for medical knowledge. So I presented myself as a medical doctor - something which even the ignorant can appreciate."
Learning to Appreciate the Kohanim
The Kohanim are charged with a key mission in the nation. They represent the nation with their service in the holy Temple. They purify and bless the people, and teach them Torah. "From the Kohen's lips they will guard knowledge, and they will seek Torah from his mouth." (Malachi 2:7).
The Kohanim also assist in the scandalous case of a wife suspected of being unfaithful. The Kohanim were part of the ceremony designed to reveal the truth of the matter, and (hopefully) restore peace within the family.
The astute recognize that Kohanim have a wide range of tasks in their mission to elevate, educate, and atone for the people. They are happy to support the Kohanim and their important work.
But a person who refuses to give tithes to the Kohanim clearly fails to appreciate what they do. Therefore Divine providence arranges that he will need the Kohanim should he doubt his wife's fidelity. Then he will begin to acknowledge the contribution of the Kohanim - at least the smallest and least noble of their functions.
(Adapted from Mishlei Yaakov pp. 313-314.)