This is the counsel of Sun Wu, a renowned ancient military thinker. The goal of war is first and foremost to protect oneself and to defeat the enemy, and conversely only by defeating the enemy can one fully protect oneself. Another way of seeing this is to recognize that effective self-protection is the precondition for defeating the enemy. That is why the commander must plan carefully, prepare for both attack and defense, and not give the enemy any chance to fulfill its military objectives.

Those who excel at war must first protect themselves from defeat, and also take every opportunity to defeat the enemy. (The Art of War)