Da Gama sailed to India in search of "Christians and spices." He was sent by the king of Portugal in order to get in on the spice trade that was largely dominated by the Italian city-states who, unlike the rest of Western Europe, had no problems dealing with Arab traders in the Mediterranean.
Da Gama also hoped to find Christians in India. The search for Christians in other parts of the world was to be a constant driving force for Western Europeans—as it was rumored that there may be Christians in Asia. If this were true, it was hoped that the Christian kingdoms of the East would link up with the kingdoms of the West and force the Arabic world into submission. This never materialized.
Da Gama, as a byproduct of his trip to India, also managed to make Portuguese claims in Africa. Portugal would later exploit these claims in order to collect gold, ivory, and slaves.
While Da Gama did not encounter any Christians in India, he did encounter Hindus who he thought were Christian. He also learned that the Hindu leaders of India were not impressed with the gifts of Portugal, eventually leading his crew to take spices by force and to rule with intimidation and threats.