This is the chapter that separates the book from every other piece of Warring States strategic writing, and it does it in one instruction. The killing of multitudes should be met with grief and mourning, and a victory should be conducted with funeral rites.
Nothing about that is advice on how to win. It concerns what to do afterwards, and it prescribes the ritual form: the ceremony that follows a successful campaign should be the ceremony for a death, not the ceremony for an achievement. In a culture where ritual form was the public statement of what an event meant, that is a substantive demand rather than a sentiment.
The chapter builds to it through the etiquette of position. In peace the gentleman honours the left; in war the right. The seating and standing order of a court encoded rank and auspiciousness, and the chapter observes that military occasions invert it, which is its evidence that a culture already treats war as belonging to the register of ill fortune even while pursuing it.
The middle of the chapter draws the line the whole passage turns on. Weapons may be used when they cannot be avoided, and calm restraint is best; but to find victory beautiful is to delight in killing, and a person who delights in killing will not get his way in the world. The condemned thing is not fighting and not winning. It is aesthetic pleasure taken in the result.
The last clause is characteristic. Even here, where the objection is plainly moral, the sentence given is a prediction about what will happen to such a person rather than a verdict on him.