Alright, so in Hebrews 3, the writer is trying to get the readers to hold fast to their faith in Jesus, and not be swayed by anything else. And he's using Moses as an example of the type of faith that they should have. He says that if the people had responded to Moses, they would have seen the promised land, but they didn't, and so they were punished. So, it's like, don't be like the Israelites and miss out on the promised land. Follow Jesus, and you won't be disappointed.