Now

This word is used here to mark a break in the main storyline. Here the narrator tells us why the gates of Jericho are closed and locked up.

I have delivered Jericho into your hand, its king, and its trained soldiers

Yahweh is telling Joshua that he will certainly do this by saying that he has already done it. (See: rc://en/ta/man/translate/figs-pastforfuture)