Light rays from a point object after refraction converge at a single point in case of 

A ray of light which is originally parallel to the principal axis passes through the focus after refraction through the lens. A ray of light is passing through optical center of convex lens doesn't bend after refraction but goes straight. Also a ray of light going along path of principal axis of convex lens also goes straight and doesn't deviate. When a ray of light passes through the focus of convex lens then it becomes parallel to the principal axis after refraction through lens.