In "The Perils of Indifference", author Elie Wiesel wants us to understand that when someone is indifferent to another person's suffering, he or she is equally guilty as the person who is causing the suffering.
Wiesel is appealing to Ethos, or appealing to ethics, when she tries to make it clear that when a person stans idle towards the suffering of another, he or she becomes an accomplice of the crime or harm committed against that person.