It's just words, but it's effective to some people. If I promise or swear something though, I will go out of my way to keep it, it's just how I work. If I say I'll do something, I'll try my hardest to do it.
It's a load of bullshit. You think anyone is going to drop dead or "burn in hell" if they tell a lie to a fucking 12 year old? I say it a lot myself. It's a good way to get people to believe you, even if what you're saying is complete bullshit.