John Calvin Commentary Isaiah 48:2

"(for they call themselves of the holy city, and stay themselves upon the God of Israel; Jehovah of hosts is his name):" — Isaiah 48:2 (ASV)

For from the holy city they are called. He continues the same subject and, using different words, exposes their false boasting; for they falsely boasted that they were citizens of “the holy city,” which they defiled by their vices and crimes. Jerusalem should have been “holy,” for God had consecrated her to himself; but she had prostrated herself to iniquities so great and numerous that she scarcely retained any holiness. We see in Psalm 15:2 and Psalm 24:4 what the true citizens of Jerusalem should be; but because the Jews were not ashamed of mocking God, they considered it enough to be protected by the shadow of the Temple.

And rely on the God of Israel. When he says that they “rely on Jehovah,” he does not speak of sincere belief, but of empty confidence. For, just as good men rely on God and trust him with their whole heart, so hypocrites falsely profess his name, are intoxicated by unfounded belief, fearlessly despise everything, and even boast confidently with these words, “God will assist us, and he will not cast off his people”; as if God wished to encourage their wickedness.

In a word, by trampling him under their feet, they loudly declare that they rely on themselves for safety. But, so that they would not think that they will not be punished for this mockery, the Prophet assures them that God loses nothing of his authority when he is thus misrepresented by hypocrites. For when the Prophet calls him Jehovah of hosts, he adds this by way of threatening, so that they might know that God, under whose name they falsely sheltered themselves, was strong enough to punish them, and eventually would not permit them to make him the subject of mockery.