It’s not a lie. Christ hung on the cross for all of our sins, not just those who accept him. In order to take advantage His Atonement, one must repent of their sins, acknowledge Christ as their Savior. For those who do not repent, they shall suffer for their own sins. But there will be an end to that suffering and then everyone will receive their reward, according to their worthiness, and the desires of their hearts. Yes, I really do believe this.