And Joshua said to the people, You cannot serve the LORD: for he is an holy God; he is a jealous God…
Their inability was wholly of the moral kind. They could not do it because they were not disposed to do it, just as it is said of Joseph's brethren (Genesis 37:4) that they "could not speak peaceably unto him," so strong was their personal dislike to him. But an inability arising from this source was obviously inexcusable, on the same grounds that a drunkard's inability to master his propensity for strong drink is inexcusable. In like manner the "cannot" of the impenitent sinner, in regard to the performance of his duty, is equally inexcusable.
Parallel VersesKJV: And Joshua said unto the people, Ye cannot serve the LORD: for he is an holy God; he is a jealous God; he will not forgive your transgressions nor your sins.