ममैवांशो जीवलोके जीवभूतः सनातनः। मनःषष्ठानीन्द्रियाणि प्रकृतिस्थानि कर्षति ॥

mamaivānśho jīva-loke jīva-bhūtaḥ sanātanaḥ manaḥ-ṣhaṣhṭhānīndriyāṇi prakṛiti-sthāni karṣhati

A portion of Mine own Self, transformed in the world of life into an immortal Spirit, draweth round itself the senses of which the mind is the sixth, veiled in matter.

In plain words: Krishna says each living soul is a small, eternal part of himself. Living in the world, it gathers around itself the five senses and the mind, and these are wrapped in matter.