In a certain country, tribal clashes occurred between two tribes but it finally came to an end. Peace prevailed but some people from the most affected tribe didn’t want to live there simply because they didn’t believe that there will be no clashes again.
In Christianity life believing in Jesus Christ matters a lot. Without believing in Him it’s impossible for you to attain eternal life. Read John 3:16. Just like the people who didn’t believe that there won’t be any clashes, there are people who don’t believe in the word of God. They have failed to claim the promise that God has promised them.