One thing I've always loved about each of the four Indy movies is each has it's own moral message or theme to the movie. In Raiders, the key theme of the film was "Don't mess with God". It shows the enormous consequences of meddling in God's business at the end of the film. In Temple of Doom, it's about doing what's right over choosing fortune and glory. I think the key moment of this film is when Indy gets his hands on the stones, and then hears the children being whipped off in the distance, and he chooses to do what's right rather than pursue the fortune and glory. In Last Crusade, it's about having faith, no matter what obstacles come in your way, even in the face of the seemingly impossible. And in Crystal Skull, it's about the pursuit of knowledge, and using the knowledge you obtain responsibly, and for good ends. Knowledge is a gift, and we are to use it for good, and there are consequences when we use it for evil.