Jñāneśvarī (commentary on the Bhagavadgītā) 4.166

4.166

je jñānācā kuruṭhā |
tetha sevā hā dāravaṃṭā |
to svādhīna karī subhaṭā |
voḷagonī ||

For they are the dwelling-place of knowledge,
and service is the threshold to it;
render that threshold your own, O great warrior,
by serving them.