God is called the Lord of Armies to signify His supreme authority over all celestial and earthly powers.
The title 'Lord of Armies' (or Lord of Hosts) underscores God's ultimate authority and power over all cosmic forces, including both heavenly beings and earthly authorities. This is illustrated in 2 Kings 6, where God opens the eyes of Elisha's servant to see the overwhelming heavenly hosts protecting them. Moreover, it signifies the assurance that God's plan will prevail against any opposition, as He commands all the forces of heaven in executing His will. This name serves to remind believers that no matter their circumstances or the threats they face, they are under the sovereign protection of God, who fights for His people and ensures that His divine purposes are accomplished.
Commentary