John Calvin Commentary Amos 5:9

"that bringeth sudden destruction upon the strong, so that destruction cometh upon the fortress." — Amos 5:9 (ASV)

The Prophet is not now speaking of the ordinary works of God, in which His majesty, inspiring the highest reverence, as well as His dread power, shines forth. Instead, he more closely urges the Israelites, who had become so hardened in their vices that they were completely inflexible. Here then the Prophet charges them with stubborn resistance and says, “What, do you think, will take place? You are strong; but God will stir up robbers against you, who will prevail, and beat down and shatter in pieces that stubbornness through which you now resist God.” Thus, after filling them with dread by setting before them the course of nature, he now presents this threat: they themselves would have to feel the power of God. For however callous they were, and though in their ferocity they dared to rise up against God, He declares that it would be of no use to them, because there was a destroyer in God’s hand who would prevail against their stubbornness.

And a waster, he says, shall ascend upon the very fortresses, or shall enter the fortresses. The Prophet here, in an indirect way, scoffs at the vain confidence that filled the Israelites when they observed that they were enclosed in fortified cities and had defenses and a powerful army. All this, he says, will be completely useless to them when God raises up strong plunderers, who will penetrate through well-fortified gates, leap over walls, and enter strongly defended cities. We now understand what the Prophet had in view in these words.

It will now be easy to apply this doctrine for our own instruction. Whenever we are not properly moved by the truth, by warnings, or by threats, let what the Prophet teaches here come to our minds: namely, that God cannot be mocked, and that hypocrites gain nothing by their delusive ceremonies when they sacrifice and present their expiations, which do not please God at all — how so? Indeed, we can easily learn the reason from the nature of God Himself. Therefore, so that we do not form a distorted image of God, let us learn to lift our eyes to behold Him, and also to look at all things around us; and this will compel us to adore and fear His great power.