The narration in Tom Jones is satirical. Satire is a type of playful, humorous criticism. The fact that Fielding uses an omniscient narrator makes this possible. The use of third person allows the narrator to not be part of the action. Omniscience makes it possible for the narrator to know and describe everything that is going on. This is how satire can be used.
Throughout the story, Fielding pinpoints social institutions and human behaviors to target. He makes fun of the vanity and hypocrisy of his characters, using his omniscience to point out his opinions. This is part of what makes the story funny and interesting, and why satire is still popular today. Think of Tom Jones as the Saturday Night Live of Fielding’s day!