Jacob was cooking a stew. That same day, Abraham had died, and Jacob was cooking a dish of lentils, in order to feed his father, Isaac. And why do they feed a mourner lentils? Because it is forbidden for a mourner to speak, and just as lentils do not have a mouth (or opening), so too mourners are forbidden to speak, as it is stated, "Aaron was silent." (Leviticus 10:3) Another interpretation: Just as lentils are round, so too death is a cycle of return in the world.
And Esau came in from the field. Five sins did Esau transgress on that day: He stole, as it is stated, "If thieves were to come to you." (Obadiah 1:5) It is written here, "come", and it is written with Esau, "come." He had relations with a betrothed woman, as it is written here, "If he finds in the field" (Deuteronomy 22:25), and it is written with Esau, "in the field." He killed someone, as it is written here, "Alas for me, I faint before the killers" (Jeremiah 4:31), and with Esau it is written, "and he was faint."
And he denied the principal, as it is written here, "he is become my deliverance" (Exodus 15:2), and with Esau it is written, "what is this to me, the birthright?" As it is stated, "thus did Esau spurn the birthright." (25:34)