“The good qualities of concentration are as follows: When you reach serenity, your mind is filled with delight and your body filled with bliss, so you are happy in this lifetime. Also, since you have attained physical and mental pliancy, you can turn your attention to any virtuous object of meditation you choose. Since you have quelled uncontrolled distraction toward the wrong sort of objects, you are not constantly involved in wrongdoing and any virtue you do is very powerful. Based on serenity, you can achieve good qualities such as the superknowledges and supernormal powers. In particular, it is on the basis of serenity that you develop the knowledge of insight that knows the real nature, whereby you can quickly cut the root of cyclic existence.”
From The Great Treatise on the Stages of the Path to Enlightenment by Je Tsong Khapa
As translated in: The Great Treatise on the Stages of the Path to Enlightenment: The Lam Rim Chen Mo by Tsong Khapa. Translated by the Lamrim Chenmo Translation Committee. Snow Lion/Shambhala Publications.