John Calvin Commentary John 9:4

"We must work the works of him that sent me, while it is day: the night cometh, when no man can work." — John 9:4 (ASV)

I must work the works of Him who has sent me. He now testifies that He has been sent for the purpose of manifesting the kindness of God in giving sight to the blind man. He also borrows a comparison from the ordinary custom of life; for when the sun has risen, man rises to labor, but the night is allotted to rest, as it is said:

The sun rises; man goes forth to his work, and to his labor, until the evening (Psalms 104:22, 23).

He therefore uses the word Day to denote the time that the Father had fixed, during which He must finish the work assigned to Him; in the same manner, any person who has been called to some public office should be employed in what may be called their daily task, to perform what the nature of their office demands.

From this, we also should deduce a universal rule: that for every person, the course of their life may be called their day. Therefore, just as the short duration of daylight should motivate laborers to industry and toil, so that the darkness of night does not surprise them before their exertions are well underway, so too, when we see that a short period of life is allotted to us, we should be ashamed of languishing in idleness.

In short, as soon as God enlightens us by calling us, we should make no delay, so that the opportunity may not be lost.