From Swami Vivekananda’s discourse at the World’s Parliament of Religions, Chicago, 26th September 1893,

The religion of the Hindus is divided into two parts: the ceremonial and the spiritual. The spiritual portion is specially studied by the monks.

In that there is no caste. A man from the highest caste and a man from the lowest may become a monk in India, and the two castes become equal. In religion there is no caste; caste is simply a social institution. Shâkya Muni himself was a monk, and it was his glory that he had the large-heartedness to bring out the truths from the hidden Vedas and through them broadcast all over the world. He was the first being in the world who brought missionarising into practice—nay, he was the first to conceive the idea of proselytising.

Source: The Complete Works of Swami Vivekananda, Also on Wikisource