http://www.chabad.org/library/bible_cdo/aid/8220/jewish/Chapter-25.htm#showrashi=true30 And Esau said to Jacob, "Pour into [me] some of this red, red [pottage], for I am faint"; he was therefore named Edom.
Rashi comments:
some of this red, red [pottage]: red lentils.
And on that day, Abraham died, lest he see Esau, his grandson, falling into bad ways, for that would not be the “good old age” that the Holy One, blessed be He, had promised him. Therefore, the Holy One, blessed be He, shortened his life by five years, for Isaac lived one hundred and eighty years, and this one (Abraham) [lived] one hundred and seventy-five years, and Jacob cooked lentils to feed the mourner (Isaac). But why lentils? Because they are [round as] a wheel, for mourning is like a wheel revolving in the world. (Also, just as lentils have no mouth [no crack], as other beans have, so does the mourner have no mouth, for he is prohibited from speaking. It is therefore the custom to feed the mourner eggs at the beginning of his meal, since they are round, and have no mouth. So too does a mourner have no mouth, as is discussed in Mo’ed Katan (21b): “A mourner, for the entire first three days, may not respond to anyone’s greeting, and may surely not initiate a greeting. From the third day to the seventh, he may respond, but may not greet, etc.” [This is found] in an old [edition of] Rashi.)- [From Gen. Rabbah 63:12, B.B. 16b]