Charles Ellicott Commentary Genesis 27:38

"And Esau said unto his father, Hast thou but one blessing, my father? Bless me, even me also, O my father. And Esau lifted up his voice, and wept." — Genesis 27:38 (ASV)

Hast thou but one blessing? — Only one son could inherit the spiritual prerogatives of the birthright, and the temporal lordship which accompanied it. And even lower earthly blessings would avail little if Esau’s descendants were to be subject to the dominion of the other brother’s race. With some mitigation, then, of his lot Esau must now be content.