Manava Dharmashastra 2.230

2.230

kāryakāraṇayorabhedādevamucyate | trayāṇāṃ lokānāṃ prāptihetutvātta eva trayo lokā ucyante | ta eva ca trayaḥ prathamādbrahmacaryādanye traya āśramāḥ | gārhasthyādibhistribhirāśramairyatphalaṃ prāpyate tattaistribhistuṣṭaiḥ | ta eva trayo vedā vedatrayajapatulyaphalatvāt | ta eva trayo'gnayaḥ | agnisādhyakarmānuṣṭhānaphalāvāptestacchuśrūṣātaḥ | eṣā'pi praśaṃsaiva |

These have been declared to be the three regions, these the three life-stages, these the three Vedas and these the three fires.—(230)

Medhātithi’s commentary (manubhāṣya):
What is stated here is on the understanding that there is no difference between the cause and its effects.

‘These have been declared to be the three regions,’—because they are the means by which one is enabled to reach the three regions.

‘These the three life-stages’—i.e., with the exception of the first, that of the Religious Student. The meaning is that the reward obtained by means of the three life-stages beginning with that of the Householder is obtained if these three persons are satisfied.

‘These the three Vedas’;—because service of them brings the same reward that is obtained by reciting the three Vedas.

‘These the three Fires’;—because the serving these brings the rewards that are obtained by the performance of acts done with the help of the three sacrificial fires.

This also is purely eulogistic.—(230)