Rāja-vidyā means the king of knowledge. If you learn this knowledge, then you become completely freed from the conditioned stage of this material world. Therefore it is called rāja. Rāja means king, and vidyā means knowledge.
Rāja-vidyā rāja-guhyam. And at the same time, it is the most confidential knowledge, guhyam, guhyatamam, very confidential. It is not disclosed to ordinary man. This knowledge is not meant for. Suppose we are discussing this knowledge, and when we say, "By understanding this knowledge there is no more birth, death, old age, and disease," ordinary person with less brain substance, they will laugh. They will say, "Ha, how it is possible?" Therefore it is very confidential. It is not open to everyone. It is meant for selected person. If I say that "I shall give you relief from birth, death, old age and disease," you'll not believe it. Therefore it is rāja-guhyam. Guhyam means very, very confidential.
Rāja-vidyā rāja-guhyaṁ pavitram. Pavitram means very pure. Because unless we are purified, we cannot be free from these four miserable conditions especially, namely birth, death, old age, and disease. Birth, death, old age is meant for this body, and the body is obtained by the spirit soul. The spirit soul is pure; there is no doubt about it because it is part and parcel of Kṛṣṇa or God. So God is pure. Just like gold is gold. And the fragments of gold is also gold, the same quality. But the fragments of gold sometimes becomes mixed up with dirty things. So we are in the same condition. Becoming fragments of God, we are sometimes put into this material world and we are materially contaminated. So this knowledge, rāja-vidyā, most confidential. If we can learn it, then we become pure, completely pure.
Pavitram idam uttamam. Uttamam. Ut mean udgata, transcendental, and tama means this material world, darkness. In the material world the nature is darkness. Just like at night it is darkness. This is the nature of this material world. But it is... There is illumination on account of the sun. So God has created the sun to give us light.