Isaiah continues speaking.
“Yahweh was appalled that no one came to help those who were suffering.” or “Yahweh was astonished that no one came to help those who were suffering.”
Yahweh’s “arm” represents his ability and power. AT: “Yahweh used his own power to save the people” (See: rc://en/ta/man/translate/figs-metonymy)
“Righteousness” here is a quality that acts like a person. The word can be translated as an adjective. AT: “he did right as he always would do” (See: rc://en/ta/man/translate/figs-personification and rc://en/ta/man/translate/figs-abstractnouns)