Manava Dharmashastra 1.86

1.86

athamanyo yugasvabhāvabhedaḥ kathyate | tapaḥprabhṛtīnāṃ vede yugabhedena vidhānābhāvātsarvadā sarvāṇyanuṣṭheyāni | ayaṃ tvanuvādo yathākathañcidākhyeyaḥ | itihāseṣu hyevaṃ varṇyate | tapaḥ pradhānaṃ tacca mahāphalam | dīrghāyuṣo rogavarjitāstapasi samarthā bhavantyanenābhiprāyeṇocyate | jñānam adhyātmaviṣayaṃ; śarīrakleśādantarniyamo nātiduṣkaraḥ | yāge tu na mahākleśa iti dvāpare yajñaḥ pradhānam | dāne tu na śarīrakleśo nāntaḥsaṃyamo na cātīva vidvattopayujyata iti susampādyatā |

In the Kṛta Cycle, ‘Austerity’ is the highest; in the Tretā ‘knowledge’ is described as such; in the Dvāpara they call the ‘Sacrifice’ the highest, and ‘Charity’ alone in the Kali-Cycle—(86).

Medhātithi’s commentary (manubhāṣya):
Another difference in the character of the Cycles is now described.

As a matter of fact, Austerity and the other Virtues are not prescribed in the Veda with reference to any particular Cycle, all of them should be performed at all times; hence the description contained in the present verse has got to be explained somehow or other. In fact it is in the Itihāsas that the distinction herein set forth is met with. [When ‘Austerity’ is relegated to the Kṛta Cycle] what is meant is that it is the principal—and hence the most effective—Virtue cultivated; and the men being longlived and free from disease are most capable of performing Austerities.

‘Knowledge’—i.e. of spiritual matters. Though the men [being not quite so healthy in the Tretā as in the Kṛta ], suffer in the body, yet this bodily suffering does not render the internal discipline (necessary for spiritual knowledge) very difficult.

In as much as there is not much trouble in the performance of Sacrifices, sacrifice forms the chief virtue in Dvāpara.

In Charity, there is neither physical suffering, nor need for internal discipline or much learning; hence it is easily done.—(86)