David is the creative power planted in every person, the anointed son who conquers death from within. The giant he stands upon is the whole weight of the outer world insisting that facts are fixed and cannot be moved. When David takes the giant's own sword and cuts off his head, the power of appearances is beaten with the very force it relied on. The mind that was ruled by what the senses report is severed from its command.
The fleeing army is every lesser doubt that scatters once its champion is gone. The battle is never a distant field. It is the moment a person's own imagination overturns the belief that things are settled against him. When that power returns victorious, death is finished, and the man knows he is the father of the son who won.