Collected on the Internet: The rabbis teach that [Esav] did perform the mitzvah of honoring his father, and he even asked his father about the need to take tithes from salt and straw - which of course is completely unnecessary, and represented Eisav's ability to appear religious when it suited his purpose.
If you've studied Rashi as an adult, you know his commentary isn't an anthology of midrashim. Frequently, Rashi cites a midrash out of place or out of context. He'll change the meaning of a midrash, or choose one or two midrashim from among several on the same subject. Rashi does all of this, I believe, because in his commentary, midrashim are used for a specific purpose, namely, they serve to smooth out rough spots in the text, and to resolve difficulties in the language of the Torah.
Rashi's object, you see, isn't to share or to popularize midrashim, but to " give... Aggadah which serve to clarify the words of Scripture in a way which fits its words" (Gen 3:8)
The midrash cited at the begining of this post is, I believe, an example of Rashi doing violence to the plain meaning of the midrash for the sake of rescuing the text from a perceived anamoly. Gen 25:28 reads: "And Issac loved Esav because of the game in his mouth." (tzayid b'fiv) This is a hebrew idiom, which suggests Esav as either a kind of lion bringing home food in his mouth, or as a mother bird dropping worms into her chick's gapping beak. In either case, it's a material and, therefore, difficult explanation for Issac's favoritism. The plain language of the text make Issac look shallow, and weak, and more than a little absurd. For Rashi, this is unacceptable. Therefore he tells us "But, its [ie tzayid b'fiv's ] Midrashic interpretation is: "With the mouth of Eisv" [meaning] he would trap him and trick him with his words
Trap him and trick him how? The answer Rashi gives appears on the previous verse, Gen 25:27, where we're told that "Esav was skilled in trapping, a man of the field, and Jacob was a simple man, a dweller in tents." The perceived anamoly here is that the second part of the descriptions ("man of the field" and "dweller in tents") are roughly atithetical; the first parts ("skilled in trapping" and "simple man") are not.
The Hebrew adjective tam suggests integrity, or even innocence. To create a diametric opposition between the first and second parts of the description, "skilled in trapping" needs to be construed as the opposite of tam. Three examples of Esav's duplicity are provided in the midrash, and Rashi chooses one, and only one, to illustrate the point, writing " ..he would ask him: "Father, how are salt and hay tithed?" [Though, he actually knew that there is no requirement that these items be tithed.] His father would thereby think that he meticulously observed the mitzvos."
I don't know why Rashi selected the bit about the straw and hay over the two other examples of Esav's dishonesty provided by the Midrash, but I will argue in the next post that the story itself has been misunderstood by readers of Rashi.