Because Kṛṣṇa is neither brāhmaṇa nor śūdra nor kṣatriya or anything, anything of the material world. He is transcendental. When we go to Kṛṣṇa with spiritual body, we also become like Kṛṣṇa in transcendental body. That chance is given here. So just it is our duty, everyone.
Lord Caitanya, He is Kṛṣṇa Himself. He appeared as a devotee of Kṛṣṇa, but He never said that "I am Kṛṣṇa." But from Vedic references we understand that He is Kṛṣṇa. But the same mission. The Kṛṣṇa's mission and Lord Caitanya's mission is the same. How it is same? Kṛṣṇa, as the Supreme Personality of Godhead, He said that "You surrender unto Me," and Lord Caitanya said, "You surrender unto Kṛṣṇa." The same thing.