Sutra 1.19

भवप्रत्ययो विदेहप्रकृतिलयानाम्॥१९॥ 
bhava-pratya-yo vide-ha-prakriti-lay-aa-naam॥19॥ 

With a few word changes, Barbara Miller says, in essence: “For Beings and beings unencumbered by physical bodies, but still enmeshed in the material or physical world, the cessation of the streams of thought is limited by reliance for all perceptions on the phenomenal world.” Sutras 17, 18 and 19 are addressing the slow cessation of mental activity as we continue to practice yoga (referring not only to the practice of the physical form of exercise, but to all eight limbs of yoga) and meditation to curb our ‘monkey mind’. This is a very simplistic way of looking at the deep significance of Patanjali’s thoughts, but it’s a worthy start.