Sometimes the birds are also called dvija. Dvija means twice-born. Twice-born. Just like the birds... The sea bird lays the egg first, and then it is fomented. And from the, I mean to, the egg, the cub comes out, the offspring comes out—the second birth. Therefore birds are also sometimes called dvija. Similarly human and higher status of life, they must have twice-born. Therefore the brāhmaṇas, the kṣatriyas, and the vaiśyas, this thread, this thread is the sign that "My second birth has been done." This is the emblem. This upavīta, upanayanam, this is the sign. In India higher caste you will find this sacred thread. Sacred thread means when he is accepted, when he is given the second birth, this thread ceremony, there is a thread ceremony. So second birth means saṁskāra, saṁskāra, reformation, reformation. It doesn't matter where and how he is born. It doesn't matter.
The other day I cited the example of Jābāli Upaniṣad. He could not say even his father's name. But because he was so sincere that he declared before Gautama Muni that "Either my mother or myself, I do not know who is my father," Gautama Muni ac..., "Oh, you are brāhmaṇa. You are truthful. You are truthful." So these are the qualifications, saṁskāra, cultural birth. Cultural birth makes the twice-born. Saṁskārād bhaved dvijaḥ. Janmanā jāyate. By birth everyone is śūdra. And when he is reformed, when he is culturally rebirth, taken rebirth, then he is dvija, twice-born. And after being dvija, veda-paṭhād bhaved vipraḥ. Veda-paṭhāt means this knowledge, scriptural knowledge, Vedic wisdom. By studying this Vedic wisdom he becomes a vipra. And after studying, when he knows, "Oh, I am spiritual. I am not this matter," and he knows the constitution of himself, constitution of the Supreme Lord, then he is brāhmaṇa. Therefore the whole mission of human society should be how to prepare brāhmaṇa. Then peace and prosperity will be there. If you keep them just like cats and dogs in the platform of śūdra, how can you expect? Do you mean to say there is any peace in the dog society? No. That is not possible. Peace can be had only, really—human society.
So this is the culture. The Vedic, whole Vedic culture is to make a man a brāhmaṇa, not to keep him in the śūdra stage, not to. Every father has to take care. The state has to take care, the teacher has to take care—how to make the children, the poor children, the innocent children, to..., a perfect brāhmaṇa. The whole culture is like that. You see? so Bhagavad-gītā teaches that. And don't become... Don't remain in the śūdra stage and a miser, but just try to become a brāhmaṇa by culture. Then your life will be successful.