John Calvin Commentary Deuteronomy 31:2

"And he said unto them, I am a hundred and twenty years old this day; I can no more go out and come in: and Jehovah hath said unto me, Thou shalt not go over this Jordan." — Deuteronomy 31:2 (ASV)

And he said unto them, I am an hundred and twenty years old. Although Moses had often been proudly and disdainfully rejected, it was nonetheless true that his departure would awaken the deepest sorrow and inspire great alarm in them. Therefore, by stating his age, he consoles their anxiety and mitigates their grief; and with another reason, he also represses their lamentations: namely, that God had fixed his term of life.

He presents this, then, as an alleviation, because his death was at a ripe age, and in his extreme old age, he was no longer fit to endure fatigue.

Here, however, the question arises: why would he say that he was failing and broken in strength, when we will see a little further on that he retained his senses in their full vigor even until his death? But the reply is obvious: he would not have been useless in his old age because his eyes were dim or his limbs trembled, but because his age no longer allowed him to perform his usual duties. For he had been marvelously and supernaturally preserved until that time; but, since he had now arrived at the end of his course, it was necessary that he should suddenly decline and be deprived of his faculties.

“To go out, and come in,” is equivalent to performing the functions of life: thus it is said in the Psalm, You have known my going out and coming in.²³¹ (Psalms 121:8). And in this sense David is said to have gone out and come in when he performed the duty entrusted to him by Saul (1 Samuel 18:5).

In the latter clause, where he refers to his exclusion from the land of Canaan and his being prevented from entering it, he indirectly rebukes the people, for whose offense God had been wrathful with himself and Aaron. Thus by this tacit reproof the Israelites were admonished to bear patiently the penalty of their ingratitude. At the same time, as he shows himself to be submissive to the divine decree, he also bids them acquiesce in it.

²³¹ C. here quotes from memory: the words of the Psalm are, “The Lord shall preserve thy going out and coming in; and so also in the other quotation, the actual words are, “And David went out whithersoever Saul sent him.”. here quotes from memory: the words of the Psalm are, “The Lord shall preserve thy going out and coming in; and so also in the other quotation, the actual words are, “And David went out whithersoever Saul sent him.”