First spiritual realization is to understand oneself that "I am not matter; I am spirit." This is the first stage of spiritual realization—when one firmly convinced. How? By knowledge. By knowledge. Just we are conscious, "I am Indian." You are conscious that you are American. One is conscious, "I am Hindu." One is conscious, "I am Christian." So similarly, when one is fully conscious that "I am spirit. Ahaṁ brahmāsmi, I am Brahman," that is the first spiritual realization, that knowledge. Knowledge means consciousness. So this consciousness has also a development of consciousness. There are different stages. And when one comes to the ultimate stages, niḥśreyasāya, that is called Kṛṣṇa consciousness, or God consciousness. And how that consciousness acts? That "I am a servant of God. I am servant of Kṛṣṇa." When this consciousness is firmly fixed up, this is called Kṛṣṇa consciousness.
Just like Caitanya Mahāprabhu, He presented Himself, nāhaṁ vipro na ca nara-patiḥ, no vanastho yatir vā. He presented Himself... Because He was Hindu and Vedic, followers of Vedic... But actually, He was not Hindu, because He's describing Himself, nāham. Nāham means "I am not, I am not." He's declining. What He's declining? "I am not brāhmaṇa, I am not kṣatriya, I am not vaiśya, I am not śūdra, I am not brahmacārī, I am not gṛhastha, I am not vānaprastha, I am not sannyāsī." The Vedic system of human life is divided into eight departmental activities, and that is going on under the name of Hinduism. It is now broken and degraded and so many things have happened. But actually, what is called Vedic system, that Vedic system is not meant for a particular class of men, but it is meant for the human society. Actually, human activities actually begins when they observe these eight principles of social divisions. More or less, they observe in any human society. What is that? Brāhmaṇa. Brāhmaṇa means the most intelligent class of men of the society. Philosophers, scientists, astronomers, so many, intelligent class. So in every society there is a class of men who are very intelligent than ordinary men. Then kṣatriya. Kṣatriya means... Kṣat means harm. One who protects others from being harmed. Suppose I am trying to harm you. And the person who protects you, he's kṣatriya. And who protects you? The king or the government. Therefore, those who are engaged in governmental affairs or takes the administrative charge, they are called kṣatriyas. So the kṣatriyas, they are in every human society, the administrator class, politicians, diplomats. Next vaiśya, mercantile class. That is not to be explained. In your country there are so many mercantile class. And śūdras. Śūdra means neither intelligent nor administrator nor merchant. General laborer. Give them something, they'll work. They have no intelligence. So they are called śūdras.