As birds flying; which come from above, and so cannot be kept off; which fly swiftly, and engage themselves Valiantly and resolutely, when they perceive that their young ones are in eminent danger. He seems to allude, and to oppose this, to those boasting expressions of the Assyrian, Isaiah 10:14: compare Deuteronomy 32:11,12 Mt 23:37. Passing over; the destroying angel shall pass over Jerusalem untouched, and shall fall upon the Assyrians. He seems to allude to the history of God's passing over and sparing the houses of the Israelites, when he slew the Egyptians, in which this word is constantly used, Exodus 12:12,23,27.
Related Commentaries of Isaiah 31:5
Isaiah 31:5
5 As birds flying, so will the LORD of hosts defend Jerusalem; defending also he will deliver it; and passing over he will preserve it.