I know not the day of my death - From his present weakness he had reason to suppose that his death could not be at any great distance, and therefore would leave no act undone which he believed it his duty to perform. He who lives not in reference to eternity, lives not at all.

And he said, behold, now I am old,.... See Gill on Genesis 27:1,

I know not the day of my death; how soon it will be; everyone knows he must die, but the day and hour he knows not, neither young nor old; and though young men may promise themselves many days and years, an old man cannot, but must or should live in the constant expectation of death.

And he said, Behold now, I am old, I know not the day of my death:

27:2 I am old, and know not the day of my death - How soon I may die.

27:1-5 The promises of the Messiah, and of the land of Canaan, had come down to Isaac. Isaac being now about 135 years of age, and his sons about 75, and not duly considering the Divine word concerning his two sons, that the elder should serve the younger, resolved to put all the honour and power that were in the promise, upon Esau his eldest son. We are very apt to take measures rather from our own reason than from Divine revelation, and thereby often miss our way.