One who does not understand the constitutional position of the body and the soul [ātmā] becomes too attached to the bodily concept of life. Consequently, because of attachment to the body and its by-products, he feels affected by union with and separation from his family, society and nation. As long as this continues, one continues his material life. [Otherwise, one is liberated.]
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यथानेवंविदो भेदो यत आत्मविपर्ययः । देहयोगवियोगौ च संसृतिर्न निवर्तते
yathānevaṃvido bhedo yata ātmaviparyayaḥ | dehayogaviyogau ca saṃsṛtirna nivartate
SB 10.4.20