The path of humanity is always coordinated with heaven and earth in the alternation of movement and stillness. Human energy is always in communion with heaven and earth in the alteration of exhalation and inhalation. – “Heaven and Earth,” c. Ming dynasty work Anthology on the Cultivation of Realiza

When the breath wanders the mind also is unsteady. But when the breath is calmed the mind too will be still, and the yogi achieves long life. Therefore, one should learn to control the breath. – Svatmarama, Hatha Yoga Pradipika