What does Isaiah 13:3 mean?

This chapter of Isaiah reveals what the Lord has shown to Isaiah about the then-future destruction of the powerful city-state of Babylon. The Lord has called for the signal to be given when it is time for an attack. He has directed those who attack to enter through the gates of the noble people of Babylon (Isaiah 13:1–2).

Now the Lord describes those attacking as His army. He says that He has consecrated these soldiers for this battle and that He commands them. The Lord is angry with Babylon. And He has summoned proud and mighty men to carry out the judgment His anger demands.

However, it is crucial to note that those attacking Babylon will not think of themselves as fighting for the God of Israel. Nor is God robotically controlling their every movement or action on a small scale. In fact, some of what these invaders do will be heinous sin that God will also judge (Mark 4:22; Matthew 12:36). He is the one arranging events so they occur this way; these nations serve His purposes despite having their own goals. God does not require the permission of anyone to determine their fate or function. He has consecrated, or "set aside for a specific purpose," this assembled army. Whatever motives they may personally have, they are attacking Babylon because the Lord wants them to.

Isaiah wrote the same about Assyria in Isaiah 10. God described the king of Assyria as the "rod of his anger." He used that king against His own people Israel even though that ruler "does not so intend, and his heart does not so think" (Isaiah 10:5–7).