The office of the Spirit, when given in ancient times, was to make manifest truth—to quicken the memory of the man of God, that he might communicate clearly things which he had once learned, but partially forgotten. For instance, the Apostles heard, during three years and a half, many sermons and a vast amount of conversation and private teaching. The office of the Spirit of truth was to bring to their remembrance the things that Jesus had formerly taught them. So it is the office of the same Spirit in these days to bring to our remembrance the words of the ancient Prophets and Apostles, and the words of Jesus, inasmuch as we have faith and confidence in God.
Orson Pratt, Journal of Discourses 6:349-50