To stop the people from fearing, Moses had made an affirmation, that the Lord himself would appear on Israel's behalf and fight for them—the first direct mention in the book of holy war. And he substantiated himself by reminding them of what they had already seen from God at the exodus.
30 L'Eternel, votre Dieu, qui marche devant vous, combattra lui-même pour vous, selon tout ce qu'il a fait pour vous sous vos yeux en Egypte,