Have you ever wondered why the title “LORD of hosts” appears more frequently in the book of Malachi than in any other OT book, or why the title appears more often in the prophetic books than in other other time period of the OT? Gordon Hugenberger has, and in the ESV Study Bible he makes an interesting observation:
In the period of Isaiah, the northern kingdom was overrun and destroyed and the southern kingdom almost destroyed by the “hosts” (armies) of Assyria. God’s people had so few troops that the Assyrian King Sennacherib could mockingly challenge King Hezekiah with the offer of a gift of 2,000 horses if Hezekiah could find enough soldiers to ride them (Isa. 36:8).
Similarly, in the period of Jeremiah, the southern kingdom was wiped out by the hosts (armies) of Babylon.
In the postexilic period of Malachi, the postage-stamp-sized Judah, as a tiny province within the vast Persian Empire, had no army of its own. It is precisely in such times, when God’s people are painfully aware of how limited their own resources are, that there is no greater comfort than the fact that the Lord has his invincible heavenly armies standing at the ready.
It is like the comfort that Elisha prayed for his servant at Dothan when they were surrounded by the Syrian armies: “‘O Lord, please open his eyes that he may see.’ So the Lord opened the eyes of the young man, and he saw, and behold, the mountain was full of horses and chariots of fire all around Elisha” (2 Kings 6:17).
Perhaps it is like the comfort felt by Jesus before the cross: “Do you think that I cannot appeal to my Father, and he will at once send me more than twelve legions of angels?” (Matt. 26:53).