Here "sword" represents an enemy army. Alternate translation: "the enemy army comes and kills anyone" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Here "blood" represents a person's death. The phrase "I will require his blood from" is an idiom that means to consider someone responsible. Alternate translation: "I will consider that person's death to be the fault of the watchman" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-idiom]])