John Calvin Commentary Joshua 24:19

"And Joshua said unto the people, Ye cannot serve Jehovah; for he is a holy God; he is a jealous God; he will not forgive your transgression nor your sins." — Joshua 24:19 (ASV)

And Joshua said to the people, Here Joshua seems to act quite absurdly by crushing the people's prompt and alert zeal, suggesting a reason for alarm. For what purpose does he insist that they cannot serve the Lord, unless it is to make them, from a sense of their complete powerlessness, give themselves up to despair and thus necessarily become estranged from the fear of God? It was necessary, however, to use this harsh form of solemn warning to rouse a sluggish people, made more lethargic by their security. And we see that this measure did not fail to achieve, at least, a momentary success. For they neither became despondent nor more lazy; instead, surmounting the obstacle, they answered boldly that they would be steadfast in performing their duty.

In short, Joshua does not deter them from serving God but only explains how rebellious and disobedient they are, so that they may learn to change their disposition. Similarly, Moses, in his song (Deuteronomy 32), when he seems to announce a separation between God and the people, does nothing more than spur and incite them, so that they may quickly change for the better.

Joshua, indeed, argues decisively from the nature of God, but what he specifically targets is the perverse behavior and untamed obstinacy of the people. He declares that Jehovah is a holy and a jealous God. This, certainly, should not by any means prevent people from worshipping Him.

However, it follows from this divine nature that impure, wicked, and profane despisers, who have no religion, provoke His anger. They can have no fellowship with Him, for they will find Him to be implacable. And when it is said that He will not spare their wickedness, no general rule is being laid down; instead, the message is directed, as often elsewhere, against their disobedient disposition.

This warning does not refer to faults in general, or to specific faults, but is confined to a flagrant denial of God, as the next verse demonstrates. Consequently, the people answer all the more readily that they will serve the Lord.