Actions are more powerful because, you can say your are going to do something but don't do it, like when this one kid said he was going to beat up my friend , but he ended up not doing it, or like when this guy owed me money and he said he was going to pay me back but he didn’t.
Another reason why actions can be more powerful than words is that you can say something to someone and it not have an impact on them, like someone can say they love you