You know the scene in Star Wars (The Empire Strikes Back) where Vader tells the Emperor that Luke will “join us or die”? It’s really not so much of a threat as it is a promise. Sure it’s a promise that he can’t keep, but Vader isn’t threatening Luke in that scene: he’s promising the Emperor that Luke will die if Luke doesn’t join them.
In a way, God has issued a similar promise to humanity: join Us or die. Except when God makes this promise He isn’t looking to scare people into a relationship with Him – He just reminds people what will happen if they choose to reject Him.