Why did Nietzsche call the Judeo-Christian ethical system a “slave morality”?

Friedrich Nietzsche characterized the Judeo-Christian ethical system as a “slave morality” because he viewed it as an ethics of the weak, rooted in envy, fear, and resentment toward the strong.12

According to Nietzsche’s genealogical analysis, the distinction between "good" and "bad" was originally a nonmoral reference to the privileged "masters" versus the base "slaves". He argued that the "slave morality" emerged when the oppressed sought vengeance by converting the attributes of the masters into vices and their own limitations into virtues. Consequently, qualities such as meekness, poverty, humility, and the act of "turning the other cheek" were elevated as moral ideals, while strength, pride, and self-affirmation were condemned as sinful or evil.31

Nietzsche believed this system undermined the human drives necessary for noble achievements and represented a "symptom of decline" or life in distress. He argued that this morality was a product of fearful personalities who sought to impose their values as absolute, thereby denigrating the natural human instinct for growth and self-affirmation, which he termed the "will to power".132