In the book Night, the message is to "Never Forget". This is the message Elie is trying to make because he constantly uses the phrases "Never will I forget" and "I remember". Elie states, "Because I remember, I despair. Because I remember, I have the duty to reject despair" (Wiesel 119). He means that we must remember the worst of the past to have a chance at a better future.
In Night, Elie says, “To forget the dead would be akin to killing them a second time.” (Wiesel xv), the meaning he is trying to convey when he says this, is that if someone has forgotten such a tragedy, it would have been the same as killing them a second time. This ties into his "Never Forget" message.