Going. Heb. se‘adah, literally, “marching.” The sound was to be to him a divine signal that God would be with him and that the armies of heaven would march before him. The masculine form se‘ad is employed in Judges 5:4 and Ps. 68:7 of the march of the hosts of God.
Bestir thyself. In the work of the Lord we must do our part. Those who sit idly by, expecting the Lord to act while they do nothing, unless the Lord has so directed, must expect defeat. God gave the word that David and his people were to bestir themselves, and promised that then He would go before them to smite the hosts of the Philistines. God’s promises, then and now, are conditional. When we do our part God will do His.