Much in the same way that Ammon taught Lamoni, Aaron begins at the level of understanding of his investigator, teaching him about the Great Spirit. The "Great Spirit" concept is not altogether wrong. Jehovah, the God of the Old Testament, surely was a Great Spirit before donning a tabernacle of flesh. Under the direction of his Father, he created all things both in heaven and in earth.
Aaron has taught the two most fundamental doctrines of the gospel: 1) that God lives, and 2) that he created the heavens and the earth. Although this may seem obvious, the fact that the creation is taught as the first distinguishing characteristic about God is significant and consistent in the scriptures. The creation of heaven and earth distinguishes God from all the pagan gods; it is the greatest single act which distinguishes Him from all imitators. The creation story is so important that it is told in latter-day scriptures in three different places and also in the temple. No other story, save the Savior's ministry and atonement, gets as much scriptural "air-time."