The Hunger Games were made to bring entertainment to the Capitol. It is also to tell people that the Capitol has great power and to scare all the Districts. Reading the book, it proves that the Capitol are heartless people who enjoy the suffering of others.
It is basically a message to the districts from the Capitol saying, "We're in absolute control over you and everything you do and we can even kill your children if we want to." It's to scare the districts into laying low instead of having another rebellion.
