John Calvin on Amos 4:6

But I gave you cleanness of teeth in all your cities, and want of bread in all your borders; and ye turned not to me, saith Jehovah. God here expostulates with the people on account of their incurable perverseness; for he had tried to restore them to the right way, not only by his word, but also by heavy punishments; but he effected nothing. This hardness doubled the guilt of that people, as they could not be subdued by God’s chastisements.

The Prophet now says, that the people had been chastised with famine, I gave them, he says, cleanness of teeth. It is a figurative expression, by which Amos means want, and he explains it himself by want of bread The whole country then labored under want and deficiency of provisions, though the land, as it is well known, was very fruitful. Now since the end of punishment is to turn men to God and his service, it is evident, when no fruit follows, that the mind is hardened in evil. Hence the Prophet shows here, that the Israelites were not only guilty, but had also pertinaciously resisted God, for their vices could be corrected by no punishment. We have just mentioned famine, another kind of punishment follows —

Amos 4:7

7. And also I have withholden the rain from you, when there were yet three months to the harvest: and I caused it to rain upon one city, and caused it not to rain upon another city: one piece was rained upon, and the piece whereupon it rained not withered.

7. Atque etiam ego prohibui a vobis pluviam, quum adhuc essent tres menses ad messem; et plui super urbem unam, et super alteram urbem non feci pluere; pars una compluebatur, et super quam non pluebat exaruit.