Manava Dharmashastra 2.218

2.218

sarvasya śuśrūṣāvidheḥ phalamidam | gurvā radhandvāreṇa svādhyāyavidhyarthavādaḥ | yathā kaścinmanuṣyaḥ khanitreṇa kuddālādinā bhūmiṃ khanan vāri prāpnoti, nākleśena, evamayaṃ vidyāṃ gurugatāṃ śuśrūṣuḥ gurusevāparo'dhigacchati |

Just as a man digging with the spade obtains water,—even so one who is eager to serve acquires the learning that is in the Teacher.—(218)

Medhātithi’s commentary (manubhāṣya):
This describes the reward in connection with the entire body of injunctions bearing upon service; and it is commendatory of learning the Veda by means of serving the Teacher.

Just as a certain man digging the earth by a spade, or some such implement, obtains water,—and he does not obtain it without trouble; similarly the pupil who is eager to serve—and attends upon him—acquires the learning that is in the Teacher.—(218)

This verse is quoted in Vīramitrodaya (Saṃskāra, p. 525) as laying down the method of acquiring learning;—and in Smṛticandrikā (Saṃskāra, p. 139) as describing the results accruing from serving the Teacher.

Comparative notes by various authors
Baudhāyana (1.2.5).—‘All Vedas enter into him who learns and behaves thus; just as fire supplied with fuel shines brightly, so shines he who knowing this follows the life of the Religious Student.’

Vyāsa Smṛti (1.36, 37).—‘In this manner, living, from day to day, on alms, the Religious Student should keep his vows; speaking agreeably, avoiding.calumny,-, always accomplishing the needs of his teacher; from beginning to end of his Vedio Study, he should constantly attend upon him; studied in this manner, the Vedic Mantra carries the Brāhmaṇa forward.’

Āpastamba Dharmasūtra (1.14.5).—‘Service of the Teacher is the only means.’

Nārada (Vīramitrodaya-Saṃskāra, p. 525).—‘Knowledge is acquired by service of the Teacher, or by much wealth, or by knowledge (in exchange); there is no fourth means;—the white ants rear up a huge heap by collecting small particles of dust: it is not strength that accomplishes this but only effort; gradually and slowly is learning acquired, gradually and slowly are riches attained, gradually and slowly is the hill ascended, gradually and slowly is the rags-cover made up; and gradually is the journey accomplished.’