Moroni decided to write what he could that “perhaps they may be of worth unto my brethren, the Lamanites, in some future day” (Moroni 1:4). He understood that having the priesthood and the Holy Ghost is foundational. There is nothing more important than that.
He started his instructional episode with the authority to give the Holy Ghost. If you do not have the Holy Ghost, how are you going to know how to choose the right? How can you have the spirit of “Peace I leave with you, my peace I give unto you” (John 14:27)? Moroni knew that, and he knew it was important to start with the Gift of the Holy Ghost, given by proper priesthood authority in a manner prescribed by and authorized by the Savior.
Following this, the Church must have priesthood holders (Moroni 3) so that the saints can partake of the sacrament (Moroni 4 and 5). Moroni gave us the prayers that the Nephites were using for blessing and partaking of the sacrament. Moroni really knew about the importance of covenant renewal: he placed the Holy Ghost at number one and priesthood at number two. We can see how he was starting with the most important points. Then chapter 6 is about meeting together, having a community, observing the Sabbath day, fasting and praying together, and teaching. Oh, how Moroni must have missed the blessings of meeting together! His being solitary and lonely is not altogether different from what we are missing these days (due to the pandemic in 2020) by not being able to enjoy the sociality of worship and serving together in our wards, classes, and quorums!