Answer and Explanation:
The reason why we must never stay silent in the face of oppression, as Wiesel explains, is that the oppressor who never suffers the consequences of his actions will never stop hurting others. When we remain silent, we fuel oppression by simply giving the oppressor the liberty to do whatever he chooses - discriminate, hurt, or even kill. When we say nothing, it is as if we are not paying attention to the atrocities being done. It is as if we are condoning with them, accepting them as an unchangeable reality:
"Neutrality helps the oppressor, never the victim. Silence encourages the tormentor, never the tormented."
By speaking up, we draw other people's attention to the issue. The more people paying attention, the more likely the oppressor is to be held accountable for his actions. Once the oppressor realizes he can suffer consequences, he stops. Perhaps we will never get to change the oppressor's heart - perhaps he will always be an unfair, prejudiced person -, but we can at least keep him from hurting others.