Eating Hot Food on Shabbat
Revach has a post about placing the eating hot food on Shabbat in the context of Rabbinic polemics against those who opposed the eating of hot food on Shabbat, beginning with the Sadducees. (hat tip) See this post from Chabad for a similar interpretation. While there is an explicit discussion of Sadducean rejection of an eruv on Shabbat (M. Eruvin 6:2 and see here), that the Sadducees refrained from using any fire on the Shabbat is not found explicitly in any source, and it was Abraham Geiger who first made that claim (see here and here). It’s nice to see Abraham Geiger’s theories being accepted by Orthodoxy.
For an example of now rejected scholarship, Louis Finkelstein saw the disagreement over the use of fire on Shabbat as a reflection of class-struggle in the Land of Israel.
We may be certain that this controversy did not arise from a disagreement among exegetes as to the meaning of the verse: “Ye shall kindle no fire throughout your habitations upon the sabbath day” (Ex. 35.3). Customs create exegesis, not exegesis customs. Particularly was this true in ancient times when customs were natural expressions of the popular soul and resisted artificial and arbitrary imposition.
A more probably explanation of this difference between the sects is that it arose naturally from the everday conditions prevailing in ancient Judea, which made the use of fire on the Sabbath superfluous for patrician farmers and absolutely essential for plebians, especially those who lived in Jerusalem.
It will be remembered tha the partrician farmers of Judea had their estates mainly in the lowland of the coastal plain or about Jericho, whereas the plebeians were confined to the highlands. Now, as anyone who has traveled in the Holy Land knows, there is a sharp difference in temperature between the plains and the hills during the rainy winter season. Jericho is always tropical, and the coastal plain, too, is warm even in December and January, when the cold in Jerusalem is distinctly uncomfortable.
(The Pharisees, vol. I, pp. 131-132)
For a discussion about the strictness of Sabbath observance found in the Dead Sea Scrolls, see here.
With regard to the Karaites, Daniel Sperber has treated this at length, discussing how parts of the Shabbat song כי אשמורה שבת should be understand within an anti-Karaitic polemical context. See his Minhagei Yisrael, vol. 7, pp. 142-154, esp. n. 7, and Mordechai Honig’s comments on pp. 155-159.