An expert geologist can understand where there is gold and by various processes can extract it from the gold ore. Similarly, a spiritually advanced person can understand how the spiritual particle exists within the body, and thus by cultivating spiritual knowledge he can attain perfection in spiritual life. However, as one who is not expert cannot understand where there is gold, a foolish person who has not cultivated spiritual knowledge cannot understand how the spirit exists within the body.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
स्वर्णं यथा ग्रावसु हेमकारः क्षेत्रेषु योगैस्तदभिज्ञ आप्नुयात् । क्षेत्रेषु देहेषु तथात्मयोगै- रध्यात्मविद्ब्रह्मगतिं लभेत
svarṇaṃ yathā grāvasu hemakāraḥ kṣetreṣu yogaistadabhijña āpnuyāt | kṣetreṣu deheṣu tathātmayogai- radhyātmavidbrahmagatiṃ labheta
SB 7.7.21