Yahweh describes this prophet as an example from the past. It is again quite likely that the referent is the singular for the plural, where the one stands for the many. Yahweh is referring to the general concept of a prophet (not a specific prophet) who has given the people teachings that would profit them and who has led the way.
Variant/Translation: The King James Version reads: “And thus saith the Lord, thy Redeemer, the Holy One of Israel; I am the Lord thy God which teacheth thee to profit.… ” The locus of the Book of Mormon change is an italicized word. In the KJV, the Lord declares, and the Lord teaches. In the Book of Mormon text, the Lord declares and also sends one to teach—but that one is “the Lord thy God,” a rephrasing that creates some confusion. This change may mean a messenger in vision acting in the name of God, but the scriptures do not normally make that kind of distinction.