The whole reason I began writing about the sons of God and the Priesthood was to get to the Book of Moses. I considered doing multiple posts on Moses 5 through 8 but have run out of steam. You can go read it if you care to. If you can understand the concept of the sons of God you will better understand the report given in Moses.
Cain was a son of God who fell. Cain was wroth, and in jealousy rebelled against God and became perdition (Moses 5:38). As a result of his rebellion, Cain was driven from the face of the Lord, and shut out from His presence (Moses 5:39, 41).
Abel, too, was a son of God. He was a keeper of sheep and was the first real type of the sacrificial Savior we see in scripture (Moses 5:17). Though he was not the first son born to Adam and Eve, yet it is clear he received the blessings of the Firstborn (Moses 5:33, 38; 6:2).
Though Adam and Eve had children before Cain and Abel, there is very little mention of them (Moses 5:2-3). It is important to consider what happened to Adam and Eve between the time they first began having children, and when Cain was born (Moses 5:3-16, 58-59). Something important happened that changed their status before the Lord God. It is somewhat buried in the text, and we tend to overlook the details. It is not until those events occur that Eve bares Cain, and then Abel.
On the other hand, when wickedness began to spread among the children of Adam and Eve, notice the appellation given them by God (Moses 5:52-56). These are they who chose not to keep the commandments of God (ibid.). God "ministered not unto them" (ibid.). This is a juxtaposition with the sons of God, unto whom God ministered.
Some time after the murder of Abel, Adam and Eve begat Seth. Seth became the Patriarchal head, after Adam. In this son, Adam rejoiced and glorified the name of God, saying, "God hath appointed me another seed, instead of Abel, whom Cain slew" (Moses 6:2). Then we read this:
"And God revealed himself unto Seth, and he rebelled not, but offered an acceptable sacrifice, like unto his brother Abel" (Moses 6:3).
Now, Adam, being moved upon by the Holy Ghost, prophesied the following:
"Now this same Priesthood, which was in the beginning, shall be in the end of the world also" (Moses 6:7).
"This same Priesthood" has reference to that which enabled Seth to receive the revelation of God; that which enabled him to become a son of God. This same Priesthood enabled a group of the generations of Adam to be chosen as High Priests to whom the Lord came prior to the death of Adam. This shall be in the end of the world also.
The genealogy that was kept and preserved in scripture was of the children of God, and not the sons of men (Moses 6:8). Notice the next man mentioned in the Patriarchal line, after Seth, was Enos (Moses 6:13). Though there were many sons and daughters born to Adam and Eve, it was Seth and then Enos that were recorded (Moses 6:11). Enos was born to a father who was a son of God. And he, Seth, had been born to Adam, who was a son of God. This is the chain.
Study Moses 5 through 8 considering the deliberate mention of both the sons of God and the sons of men. Look for differentiation between the daughters of men, and the daughters of the sons of God. It will open up the meaning for you.