And he (the man) said, Let me go (literally, send me away; meaning that he yielded the victory to Jacob, adding as a reason for his desire to depart), for the day breaketh—literally, for the morning or the dawn ascendeth; and therefore it is time for thee to proceed to other duties (Wilet, Clarke, Murphy), e.
g. to meet Esau and appease his anger ('Speaker's Commentary'). Perhaps also the angel was unwilling that the vision which was meant for Jacob only should be seen by others (Pererius), or even that his own glory should be beheld by Jacob (Ainsworth).
Calvin thinks the language was so shaped as to lead Jacob to infer nocturna visions se divinitus fuisse edoctum. And he said, I will not let thee go, except thou bless me. The words show that Jacob now clearly recognized his mysterious Antagonist to be Divine, and sought to obtain from him the blessing which he had previously stolen from his aged father by craft.