The Roman Catholic Christian missionaries [in the Americas and in the Philippines] disregarded the Spanish secular authorities’ injunction to impose the Castilian language on the Indians as the medium of religious instruction. In their single-minded concern to preach the Gospel, the missionaries refused to be diverted by raison d’état from taking the shortest way to reach the Indians’ hearts. Even in the Philippines, where there was no pre-Castilian lingua franca, they learnt, and preached in, the local languages; and they went much farther in the Viceroyalty of Peru, where a native lingua franca had already been put into currency by the Spanish conquerors’ Inca predecessors. The missionaries in Peru reduced this Quichua lingua franca to writing in the Latin Alphabet; in A.D. 1576 a chair of Quichua was founded at the University of Lima, where it was maintained until A.D. 1770; and in 1680 a knowledge of Quichua was made an obligatory qualification for any candidate for ordination in Peru to the Roman Catholic Christian priesthood.
The Inca, unlike the Aztecs, had not had a writing system.
An Historian’s Approach to Religion, OUP, 1956