The amount of lift generated by the wing increases as airspeed increases, it also increase with angle of attack. On the takeoff roll the lift increases as the airplane accelerates.

As the lift approaches that needed for the airplane to fly ( > than the weight of the airplane) the pilot rotates the nose up slightly, which increases angle of attack providing a sudden boost in lift which pulls the airplane off the runway.

If you just kept accelerating without rotating the airplane would also eventually takeoff when the lift got high enough but it would require a longer runway and would not be elegant...the airplane might bounce down the runway a little bit first.

Most of the lift comes from the airspeed, the rotation is just done to provide a clean and decisive takeoff point and reduce runway length..