The slave revolt in morals begins by rancor turning creative and giving birth to values -- the rancor of beings who, deprived of the direct outlet of action, compensate by an imaginary vengeance. All truly noble morality grows out of triumphant self-affirmation. Slave ethics, on the other hand begins by saying no to an "outside," an "other," a non-self, and that no is its creative act. (Genealogy of Morals)In other words, in order to affirmatively and spontaneously apply the Golden Rule compassionately, as Armstrong suggests, one must first overcome one's resentments and sense of isolation. The sense that one is a victim and that the "other" is to blame is one of the worst sorts of despair and leads only to suffering and violence through the logic of subject/object.
By contrast the "triumphant self-affirmation" is not egotistic or self-regarding, but, as he says in The Birth of Tragedy, an "'I' dwelling, truly and eternally, in the ground of being." Nietzsche uses words like "noble", "aristocratic" and "heroic" to describe this quality, but these are just metaphors he uses for the artist. He's not celebrating feudalism or warfare (or nihilism or fascism), but using those fanciful phrases to engage the reader with the abstract possibilities of art and philosophy. His affirmation is like Molly Bloom with her "yes, I will, yes", and like Kierkegaard's tortured logic that leads to the self resting transparently in the spirit that gives it rise as a cure for the sickness unto death (despair). It is a rhetorical leap of faith into the creative possibilities of the imagination.