Atonement in Christianity is when Jesus died on the cross. It means that through his death, our sins are forgiven and we can be made right with God. Jesus was God's son and he loved us so much that he was willing to give up his life so we could be with God. When Jesus died, he made it possible for everyone to be forgiven and to have new, better lives. So through Jesus' atonement, God can forgive us and we can be with him forever.