Jamieson, Fausset and Brown on Genesis 32:26

26. I will not let thee go, except thou bless me--It is evident that Jacob was aware of the character of Him with whom he wrestled; and, believing that His power, though by far superior to human, was yet limited by His promise to do him good, he determined not to lose the golden opportunity of securing a blessing. And nothing gives God greater pleasure than to see the hearts of His people firmly adhering to Him.