Charles Ellicott Commentary Genesis 32:26

"And he said, Let me go, for the day breaketh. And he said, I will not let thee go, except thou bless me." — Genesis 32:26 (ASV)

Let me go — Hebrew: send me away, for the gleam of morning has gone up. The asking of permission to depart was the acknowledgment of defeat. The struggle had to end at daybreak, because Jacob now needed to attend to his duty; and the wrestling had been for the purpose of giving him courage, and enabling him to meet danger and difficulty in the power of faith. A curious Jewish idea is that the angel was the one whose duty it was to defend and protect Esau. With the aid of his own protecting angel, Jacob, they say, had overpowered him and had won the birthright and the precedence as Israel, a prince with God and man.

Except you bless me. — The vanquished must yield the spoil to the victor; and Jacob, having gradually become aware that the one wrestling with him was more than human, asks him for a blessing as his ransom.