Esau said in his heart

Here "heart" stands for Esau himself. AT: "Esau said to himself" (See: rc://en/ta/man/translate/figs-synecdoche)

days of mourning for my father are near

This refers to a number of days a person grieves when a family member dies.

This can be stated in active form. AT: "Someone told Rebekah about Esau's plan" (See: rc://en/ta/man/translate/figs-activepassive)

"Look" or "Listen" or "Pay attention to what I am about to tell you"

"is making himself feel better"