Give me some of that red stuff. He said to Jacob, I will open my mouth and you can throw it in like a pot. This is like we learned about filling up a camel when one wants to go on a far journey. From this red stuff.
About himself he said "red", as it is stated, "the first came out ruddy." Because on that very day that Esau sinned five times, Abraham died, just as the Holy One Blessed Be God had promised him, that he would be buried in good old age. And this is a good old age, that he (not) see his grandson go out to an evil culture. And about Esau it is stated, "be ever mindful of his father's iniquity." (Psalms 109:14) That he caused Abraham's death and dimmed the eyes of his father, Isaac.
Another interpretation: Sell that day. Just as the day is clear, so too will your sale be clear. And why did Jacob want to buy the birthright? Because from the beginning, the avodah was for the first-borns and not the simple ones.
Jacob said, I am a simple one and I cannot do offerings. And Esau, my brother, is a wicked one and he is not fit to do offerings. Therefore, Jacob bought the birthright from Esau in order to be able to do offerings.