Charles H. Spurgeon on Psalms 78:20

Behold, he smote the rock, that the waters gushed out, and the streams overflowed. They admit what he had done, and yet, with superabundant folly and insolence, demand further proofs of his omnipotence. Can he give bread also? can he provide flesh for his people? As if the manna were nothing, as if animal food alone was true nourishment for men. If they had argued, "can he not give flesh?" the argument would have been reasonable, but they ran into insanity; when, having seen many marvels of omnipotence, they dared to insinuate that other things were beyond the divine power. Yet, in this also, we have imitated their senseless conduct. Each new difficulty has excited fresh incredulity. We are still fools and slow of heart to believe our God, and this is a fault to be bemoaned with deepest penitence. For this cause the Lord is often wroth with us and chastens us sorely; for unbelief has in it a degree of provocation of the highest kind.