Prabhupāda:
- sa vai puṁsāṁ paro dharmo
- yato bhaktir adhokṣaje
- ahaituky apratihatā
- yayātmā suprasīdati
- (SB 1.2.6)
You can read this purport.
Pradyumna: "In this statement, Śrī Sūta Gosvāmī answers the first question of the sages of Naimiṣāraṇya. The sages asked him to summarize the whole range of revealed scriptures and present the most essential part, so that fallen people, or the people in general, might easily take it up. The Vedas prescribe two different types of occupation for the human beings. One is called the pravṛtti-mārga, or the path of sense enjoyment, and the other is called the nivṛtti-mārga."
Prabhupāda: So both things are there, pravṛtti-mārga, nivṛtti-mārga. Because all the living entities who have come in this material world with a pravṛtti, with an intention to enjoy this material world. Therefore they are regulated: "All right, you want this material enjoyment?" Material enjoyment means eating, sleeping, mating and defending. That is material enjoyment. Eating, first-class eating, first-class sleeping, first-class sex, sexual intercourse, and first-class defending. So Vedic injunction is "All right, you want sex life?" "Yes, sir. For this purpose I have come here." "All right, you get your sex life by marriage, not like cats and dogs." This is called pravṛtti-mārga. He has got the intention, but he's being regulated so that one day he'll become nivṛtti-mārga.
There are two ways: nivṛtti-mārga and pravṛtti-mārga. Pravṛtti-mārga means he has got intention, desire for material enjoyment. So he's regulated, "Do like this," so that he may come to the point of nivṛtti-mārga. Nivṛttis tu mahā-phalā, pravṛttir eṣā bhūtānām (Manu-saṁhitā). Everyone has got these desires. That is pravṛtti. But when he stops this pravṛtti, that is his great achievement. Not that to increase. When he stops. That is great achievement.
So the Vedas, why one should follow? Just like Vedas says you marry. People will argue, "What is the difference of sex life marrying or not marrying? Why it is Vedas?" No. They do not know the purpose of the Vedas. The purpose of Vedas is to gradually to bring him to the point of nivṛtti. Nivṛtti, he has to make. When he has got a slight desire for material enjoyment, he'll have to accept another body. Therefore nivṛtti is required. But one cannot come to the point of nivṛtti all of a sudden. Therefore Vedic injunction is gradually bring him to the nivṛtti-mārga.