The purpose of commercials can include several objectives: to persuade, to inform, to entertain, and to educate. Each commercial may focus on one or more of these purposes depending on its content and target audience.
If you are looking for a single best answer, "to persuade" is often considered the primary goal of most commercials, as they aim to influence consumer behavior and encourage purchases. However, informing, entertaining, and educating can also be essential aspects of many commercials.