Lord Caitanya says that in the Satya-yuga this incarnation of God in white color, He preached meditation, dhyana. Therefore meditation is for the Satya-yuga. Satya-yuga means when cent percent people are pure. That is called Satya-yuga. And Treta-yuga means 75% are pure, 25% impure. And Dvapara-yuga means 50%, 50% pure and 50%… And Kali-yuga means 75% impure and 25% may be pure. (laughter) This is Kali-yuga. And we are thinking we are advancing. Such a foolish civilization, they are less than 25% pure, they do not know what is purity, and they think that they are advancing in civilization. Civilization means to purify. The Aryans, Aryans means advance. And what way advance? Advance in eating? Advance in sleeping? No. Advance in purification. They are called Aryans. And the most advanced purified is called the brahmana. And less than that, the ksatriya.

Srila Prabhupada, Lecture on CC Madhya-lila 20.330-335 — New York, December 23, 1966