In this passage, the Prophet rebukes Israel not merely for her faithlessness and idolatry but for her greed, avarice, and selfishness. We are used to the Prophets blasting Israel for the former two, but unless we pay attention (especially to some of the minor prophets like Amos) we miss or gloss over God's consistent criticism of the latter. Perhaps we honestly miss it, perhaps we skim through these rebukes because they hit close to home in our opulent American society where nearly everyone is wealthy compared to the rest of the world. As St. Augustine points out, "We [i.e. the church] are the house of Israel," so we ignore God's call through the Prophets at our own peril.
Our land is full of silver and gold. In our land, there is no limit to our treasures. Our land is full of wealth and excess...and if we are honest, we must concede our tendency to worship what we have made, our own self-reliance, or our nation which we hold dear. "Someone might ask, what is wrong with having silver or horses, particularly when what the people believed was not rigorous? How should we respond? The prophet was not criticizing the use of these possessions but the misuse of them. When he said, 'Woe to the mighty,' he was not condemning them for having possessions but for hoarding so much more than they needed" (Chrysostom, Commentary on Isaiah). To suggest that St. John Chrysostom's words do not speak directly to us is to hide our heads in the sand in willful disregard.
We should surely be thankful for the multitude of blessings we have, but at the same time, we must not let those blessings take the place in our hearts of the God who has given them to us in his great mercy.