What does Deuteronomy 9:3 mean?

But you need to know this: The Lord your God is going ahead of you like a raging fire. He’ll destroy them and bring them down in front of you. You’ll drive them out and wipe them out quickly, just like God promised you. Deuteronomy 9:3 - Modern Text Bible

(Moses reassures them that God himself will fight for them, making victory possible even when it looks hopeless.)