In the last days of Jehovah’s coming domination over all the earth, those idols that the children of Israel had thought so great will be demolished. Those who worshipped them, and those who have otherwise gone astray, will attempt to hide from Jehovah in caves. This reprises the earlier statement in verse 10 that the wicked would hide in the rocks.
When Isaiah concludes “cease ye from man, whose breath is in his nostrils,” he is admonishing Israel, and us, to cease from exalting the things of humankind—to cease from admiring worldly riches, and worldly wealth. That “his breath is in his nostrils” indicates that such men and women are mortal, and that, in contrast, the Jehovah is eternal. We are not to trade the things of eternal worth for those of temporary comfort.