"Tom Bombadil is a merry fellow! Bright Blue his jacket is, and his boots are yellow!"
Tom Bombadil embodies the goodness of the natural world. In many ways, Tom can be seen as a character foil to Sauron, the Deceiver. Where Sauron has corrupted the land, twisted life to evil, and created ruin and strife, Tom Bombadil lives and dwells among nature and the goodness of the earth. His existence is harmonious and generous, which is proven in the incident where Tom comes into contact with the Ring, but is not affected by its evil power. Evil has no meaning to Tom, because he epitomizes the wholesomeness of the natural world in Middle Earth.
Tom Bombadil represents the good in the world. He is a happy merry fellow and lives among the nature of the world. He even comes in contact with the ring at one given moment, but this does not affect him. Evil cannot be found within Tom, nor affect him, and he loves Middle Earth and nature.