Sotah

The Pasuk says: דַּבֵּר אֶל בְּנֵי יִשְׂרָאֵל וְאָמַרְתָּ אֲלֵהֶם אִישׁ אִישׁ כִּי תִשְׂטֶה אִשְׁתּוֹ וּמָעֲלָה בוֹ מָעַל

Rashi adds: שנו רבותינו אין המנאפין נואפין עד שתכנס בהן רוח שטות

What does this really mean? What kind of רוח שטות? Do people become possessed before they do an aveira? Why can't it be that people who have Bechira sometimes just not be able to fight it?

Rashi also brings down:

 איש איש כי תשטה אשתו: מה כתיב למעלה מן הענין ואיש את קדשיו לו יהיו, אם אתה מעכב מתנות הכהן, חייך שתצטרך לבא אצלו להביא לו את הסוטה

Now this seems really strange, what does מתנות הכהן have to do with a person's wife straying?

The Husband-Wife relationship is built upon a dynamic that brings the both together. In a normal healthy society the way this relationship should be built is upon the basic needs of humankind. Man wants a dedicated wife, a woman needs support and love. There is a fundamental difference between the needs of the male and the needs of the female based on their intrinsic DNA. A woman needs, as the Torah obligates, She'er, Ksus, and Onah. Food, housing and loving attention. A woman does NOT need total dedication as we know a man can have multiple wives as long as he can provide for all of them their necessities. A man on the other hand, does not need a provider as he is capable of providing for himself but rather needs total dedication. Based on this underlying marriage contract, the definition of breaking the contract is vastly different. A woman's violation of the marriage contract would be caused by her being with another man which violates her promise of dedication. A man's violation of the marriage contract would be caused by the man not providing for his wife (time and money) which is his binding commitment to the marriage. 

A רוח שטות means, not a spiritual possession, but rather probably means what it seems to mean literally, שטות, a foolishness. Hardly anybody ever walks around saying or thinking "Hey I'm a Rasha or I'm a really really bad person" but rather people tend to justify their actions. If a person does an Aveira they tend to explain it away by saying that it wasn't really bad or that there was some kind of extenuating circumstance. That is the רוח שטות that Chaza"l were referring to. No man sins if he doesn't have a foolish justification. 

Typically the justification to one partner straying within the context of a marriage is if the straying partner feels that the other party violated the marriage and that gives them a right to do what they want as the covenant has already been broken. 

The Parsha of Sotah starts with וְאִישׁ אֶת קֳדָשָׁיו לוֹ יִהְיוּ אִישׁ אֲשֶׁר יִתֵּן לַכֹּהֵן לוֹ יִהְיֶה Rashi goes on to state:

ואיש את קדשיו לו יהיו: לפי שנאמרו מתנות כהונה ולויה יכול יבואו ויטלום בזרוע, תלמוד לומר ואיש את קדשיו לו יהיו, מגיד שטובת הנאתן לבעלים, ועוד מדרשים הרבה דרשו בו בספרי. ומדרש אגדה ואיש את קדשיו לו יהיו, מי שמעכב מעשרותיו ואינו נותנן, לו יהיו המעשרות, סוף שאין שדהו עושה אלא אחד מעשרה שהיתה למודה לעשות

And furthermore:


 איש איש כי תשטה אשתו: מה כתיב למעלה מן הענין ואיש את קדשיו לו יהיו, אם אתה מעכב מתנות הכהן, חייך שתצטרך לבא אצלו להביא לו את הסוטה

The subject here is how a man spends his money and who HE thinks he can give it to and when. The Kohen is an example but what if a person doesn't spend his money correctly and doesn't give his wife what she needs thinking that it's his money and he can spend it how he wants. The ramification of that will be that his wife will feel violated and stray justifying her actions by saying to herself that the marriage covenant has already been broken. It is a natural reaction. Although, as the saying goes, 'Two wrongs don't make a right" it is a natural impulse that if your spouse "cheats" the impulse is to feel that you can cheat too. 

This is what the Pesukim and Rashi are telling us. If a man doesn't spend his money correctly and doesn't support whomever he has to support the affected party will feel "cheated upon" and justifiably so. The outcome of that will be that the wife will get affected by a "Ruach Shtus" and justify going out of bounds of her commitment. Therefore a man must do whats' right so that all people in his life will not feel the justification to reciprocate.