Why did the king of Spain sent the catholic priests to teach native Americans?

Spanish missionaries were deployed all over Central America, and as far north as Colorado and along the coast of California to spread the teachings of Catholicism. Spain's main reason for doing this was because it was easier to convert people rather than to fight them. Since Spain's goal was to secure as much territory as possible in the New World, the most effecient way to control the peoples and lands was implemented.