What does 1 Chronicles 14:12 mean?

When you hear the sound of marching in the tops of the balsam trees, move out quickly. That will mean God has gone ahead of you to strike down the Philistine army. 1 Chronicles 14:12 - Modern Text Bible

(God gave David a sign to watch for. The sound in the trees would mean God was leading the charge, and that was the moment to attack.)