Knowledge of past and future lives unfolds when one is free from greed for possessions.

Verse 2.39

अपरिग्रहस्थैर्ये जन्मकथंता संबोधः ॥३९॥

aparigraha-sthairye janma-kathaṁtā saṁbodhaḥ ॥39॥

Knowledge of past and future lives unfolds when one is free from greed for possessions.

Verse 2.40

शौचात् स्वाङ्गजुगुप्सा परैरसंसर्गः ॥४०॥

śaucāt svāṅga-jugupsā parairasaṁsargaḥ ॥40॥

Cleanliness of body and mind develops disinterest in contact with others for

self-gratification.

When one is steady in living without surplus possessions and without greed, one realizes the true meaning of one's life, and all life unfolds before one.

Perseverance in this austerity leads to knowledge of one's past and future lives which appear like reflections in a mirror. When the sadhaka i s free of worldly aspirations, he is a krtarthan (a happy and satisfied person).

Aparigraha means not only non-possession and non-acceptance of gifts, but also freedom from rigidity of thought. 

Holding on to one's thoughts is also a form of possessiveness, and thoughts, as well as material possessions, should be shunned. Otherwise they leave strong impressions on the consciousness and become seeds to manifest in future lives. 

These cycles of life continue until the sadhaka is totally clean and clear in thoughts, words and deeds.

Aparigraha is the subtlest aspect of yama, and difficult to master. Yet, repeated attempts must be made to gain pure knowledge of 'what I am' and

'what I am meant for'.

This discriminative thinking helps one to plan one's future lives from this present life.

Purity and cleanliness protect the body and make it a fit home for the seer.

Consequently it no longer leans towards sensual pleasures and tends to refrain from contact with other bodies.

Although he recognizes that the body is perishable, the sadhaka does not regard it with disgust or distaste, but keeps it clean and pure out of respect for the dweller, purusha, within. To that extent, he respects the body as a temple.

As a temple is kept clean each day, the inner body, the temple of the soul, should be bathed with Asanas and pranayama. 

They cleanse the body physically, physiologically and intellectually. The body, having its own intelligence, develops its potential to change its behavioural patterns. It helps the sadhaka to detach himself from sensual desires, and guides him towards the holder of the body, the soul.

Thus, sauca, cleanliness makes the body a fit instrument for the pursuit of spiritual knowledge.

PATANJALI YOGA SUTRAS