Formerly, there was no need of book. Therefore our Vedic literatures are known as śruti. The student will hear from the master, from the teacher, śruti. Tad-vijñānārthaṁ sa gurum eva abhigacchet, śrotriyaṁ brahma-niṣṭham (MU 1.2.12).
Simply by hearing, they'll remember. That was going on up to the date of Vyāsadeva, five thousand years ago. There was no writing principle. There was no need of writing. People were so much powerful in their memory, they could immediately remember everything by hearing once from the teacher.
Then Vyāsadeva, when he saw the Kali-yuga is coming, people's memory will be not so sharp, then he wrote all these Vedic literature. He's called Veda-vyāsa. Vedic knowledge was already there by tradition, by hearing, but he chronologically wrote all these Vedas.
So there are so many symptoms. I may explain some of them. Kālena balinā rājan naṅkṣyaty āyur balaṁ smṛtiḥ: "These things will be reduced: dharma, truthfulness, cleanliness, and forgiveness and mercifulness." People are not very merciful now. Especially in the Western countries, if one is attacked by another, people will pass. Nobody will care for that.
He may be killed. People do not show any mercy. And kṣamā. Kṣamā means forgiveness. That is also being reduced. Memory reduced, merciful reduced, span of life reduced, bodily strength reduced, health is reduced. This is the symptom of Kali-yuga.
So . . . vittam eva kalau nṛṇāṁ janmācāra-guṇodayaḥ. Formerly, there were divisions. Cātur-varṇyaṁ mayā sṛṣṭaṁ guṇa-karma-vibhāgaśaḥ (BG 4.13). The four social division: brāhmin, kṣatriya, vaiśya, śūdra. And they were calculated according to guṇa and karma, quality and work. brāhmin means he must be truthful, he must be very clean, satya śaucam.
He must be controlling his mind, controlling his senses, śamo damas titikṣa. He must be tolerant. Titikṣa ārjava. He must be simple. Ārjava, jñānam, he must have full knowledge; vijñānam, practical application in life. Vijñānam āstikyam. Āstikyam means to accept the Vedic principle as truth. That is called āstikyam. Theism. It is translated as "theism," but it is not āstika. Āstikya means to have firm faith in the Vedic instruction. That is called āstikyam.
But that is a fact. What is stated in the Vedas, they are true. We can save our time. For example, just like the cow dung. The cow dung is said in the Vedas as pure. So if we accept cow dung as pure, we don't require to make research. But actually it is pure. The other day I was passing through a cowshed in Hyderabad. So, so much cow dung was stocked there. So I was asking my students, "Suppose so much human stool was stocked here. Could we pass through it?" No, it is not possible. But it was pleasant to pass through. So this is a fact.