How do we know that we won’t be punished for our beliefs when we die?

We can’t know what will happen after we die - unless we are told by God. God has come in the person of Jesus and he has told us that if we trust in him we will have eternal life forever. John 3:16 ‘For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.’ Jesus has died and been raised - we can trust what he says.