lol.“好人” means someone that is kind."一生平安" means ba safe and peaceful during one's whole life.In this way,"好人一生平安" means" the kind will live a peaceful and safe life." This is a kind of blessings in Chinese,you can use it when others help you.For example: "谢谢你帮助了我,好人一生平安。"
I hope it helps ;)