[Note: This week's Haveil Havalim is here.]
As always: Easier to understand this with the gemara in front of you. And see Rashi. And Tosafot. And the Maharsha.
The gemara suggests that Yehudah's admission of his involvement with Tamar led to Reuven's admission of his error with Bilhah.
The Bach (note א) points out the problem put forth by Tosafot Bava Kama 92: The midrash says Reuven returned to Yosef's pit (and found Yosef had been sold) after his penance for what happened with Bilhah – but the Torah's account of Yehudah/Tamar is presented only after the sale of Yosef!
We might answer this based on the contention of Ibn Ezra (Bereishit 38:1) that the incident with Tamar happened long before the sale of Yosef. Rashi on the chumash seems to say the same.
However, this approach does run counter to the gemara's view that the whole Yehudah/Tamar story occurred during the 20 years from the sale of Yosef through the time when the brothers descended to Egypt for food.
On the bottom of the page, Abbaye seeks to solve a problem by emending a text, or having us read it non-literally – and Rava opposes his approach on the grounds of the existing text. The same will happen again on 8b and on 11a.
R' Shimon's controversial position of dorshin taama d'kra, that we may analyze laws for their underlying logic and reasons, and then use that logical analysis to alter the way we apply the mitzvah, is invoked here. For more on this see the main discussion in Bava Metzia 115a on taking collateral from a wealthy widow. See also Tosafot ahead on 14a “kedei.”
The issue of ein osin mitzvot chavilot chavilot is problematic; it seems to militate against using a single object for multiple mitzvot, but we certainly do that, as in the case of using one cup of wine for kiddush and havdalah when Shabbos leads into Yom Tov.
It appears, as noted by Rashi here, that the main issue is preventing the impression that the mitzvah is burdensome.
Further on the same topic, Tosafot והא objects that our gemara is discussing biblical verses and principles, and the idea of chavilot chavilot is d'rabbanan and should not be invoked. Perhaps we could answer that the gemara's question was actually not from that braita about chavilot/chavilot, but rather was against that braita, from the אותה source in the biblical sentence? Admittedly, though, this would be tough to fit into the words of our gemara.
Rabbah says we worry that if the sotah appears less-than-garbed in court and emerges innocent, then those who saw her in her less-than-garbed state will be drawn after her. But if she is innocent, then why don't we worry about embarrassing her?! I think this goes back to the point we made at the start of Sotah - that she is not innocent, for we know that she was alone with another man. The only question is whether that resulted in actual adultery.
Rava comments that men are visually stimulated, and less likely to be drawn by that which they have imagined but not seen. Aside from the generally interesting character of this comment, it has interesting ramifications for the issue of kol isha with a radio or taped voice.
The gemara says that women are “obligated” to come see the Sotah, but note the Rambam's formulation as to who must come see.
It's interesting that our mishnah and Rava use the same pasuk, but our mishnah concludes “permitted” and Rava concludes “obligated.”
See Tosafot Manimin on the status of national identity (Amon, Moav, Egypt) today.
The measure-for-measure with the serpent of Eden is less precise than with others in this gemara – it's that he tried to take more than he had, and so he lost even what he had.
Note: The snake thought he could get Chavah for himself because he thought the command about the fruit was just for Adam, so that she would eat and survive, and Adam would eat and die.