This is symbolic language to indicate that the angel was sent from Yahweh in heaven to judge the people on the earth. (See: [[rc://en/ta/man/translate/writing-symlanguage]])
The angel holding a sword in his hand is a symbolic action that shows he is ready to attack Jerusalem. This is symbolic, because the judgment was sickness. AT: "holding a sword in his hand as if ready to attack Jerusalem" (See: [[rc://en/ta/man/translate/translate-symaction]])