One interpretation of the Lord's army is that they are heavenly hosts. They have come literally 'from the end of heaven', and they represent 'the weapons of his indignation' (v. 5). This interpretation is not inconsistent with other scriptures of the armies of the Lord. The heavenly host was sent to protect the prophet Elisha from the king of Syria. As Elisha reassured his servant, 'he answered, Fear not: for they that be with us are more than they that be with them. And Elisha prayed, and said, Lord I pray thee, open his eyes, that he may see. And the Lord opened the eyes of the young man; and he saw: and behold, the mountain was full of horses and chariots of fire round about Elisha' (2 Kings 6:16-17). In the destruction of the last days, angels will be commissioned to bring destruction upon the wicked. The Lord explained that the angels are anxiously awaiting the opportunity to go forth in the earth, 'the angels are crying unto the Lord day and night, who are ready and waiting to be sent forth to reap down the fields' (DC 86:5). The book of Revelation makes it clear that the Lord's army, the angels, will be given specific power to destroy men in certain predetermined ways.
The literal interpretation of this verse would mean the multitudes gathered against Babylon are the armies of the Medes and Persians. The "Medes and Persians under Cyrus the Great dammed the Euphrates River and marched through the riverbed and under the walls of Babylon to capture the city and overthrow the empire. The significance of the incident is more clearly indicated by considering the imagery of the term Babylon in a spiritual sense. The call is for the 'sanctified ones' (Isa 13:2), the Saints of the latter days, to gather together and join with God in overthrowing wickedness (Babylon) from the world." (1981 Old Testament Institute Manual, p. 153)