What does Genesis 27:35 mean?

In a terrible moment that left old Isaac visibly shaken and Esau crying out bitterly, it has become clear that someone has stolen Esau's blessing. Esau has asked desperately—but futilely—that his father bless him, as well. Earlier, Esau had been so careless about his firstborn status that he'd made an oath to sell his birthright to his younger twin brother, Jacob (Genesis 25:29–34). Now, when he realizes that he truly has lost something valuable, he responds with what starts and panic, but soon turns into murderous rage (Genesis 27:41).

Now Isaac makes it clear: He knows who stole the blessing. It was Jacob. He came in deception and tricked Isaac into giving the blessing to him (Genesis 27:15–17). Whether Isaac knows, yet, that Rebekah was involved in this elaborate scheme, we don't know, but it's safe to say he will find out, eventually. For now, though, Isaac has to tell Esau that even though he doesn't like what Jacob has done, the transaction is completed. It cannot be reversed.