Moroni writes that,
Akish did administer unto them the oaths which were given by them of old who also sought power, which had been handed down even from Cain . . . And it came to pass that they all sware unto him, by the God of heaven, and also by the heavens, and also by the earth" (Ether 8:15,14).
According to Hugh Nibley, the oath was the cornerstone of the Asiatic state of the Jaredite. The reader should note that these terrible oaths are traced back explicitly to the Old World. The very oldest texts in "the oldest language in the world," according to Hommel, are incantations" having the stereotyped conclusion: 'let it be sworn (or conjured) by the name of heaven, let it be sworn by the name of earth!" [Hugh Nibley, The World of the Jaredites, pp. 200-201]
According to J.N. Washburn, we do not find mention of the oath of Cain in the Bible. We do, however, find in the New Testament what the Savior had to say about oaths and swearing in Matthew 5:34-36:
Swear not at all; neither by heaven; for it is God's throne: neither by the earth; for it is his footstool: neither by Jerusalem; for it is the city of the great King. Neither shalt thou swear by the head, because thou canst not make one hair white or black.
Anyone who, at this point, questions the authenticity of the Book of Mormon, should stop for a moment to think about the foregoing circumstance. Did Joseph Smith invent the oath of Cain? And how did he manage it so that it goes directly contrary to Jesus' admonitions with regard to swearing? [J.N. Washburn, The Miracle of the Book of Mormon, p. 169]
“The Oaths Which Were Given by Them of Old”
According to John Heinerman, to understand the oaths and covenants which bound the fraternal order of Gadianton brethren together, one must go back to an even earlier period in earth's long history. For, as Giddianhi observed in his infamous epistle to Lachoneus, "[Our] society and [its] works are of ancient date and have been handed down unto us." The Book of Mormon is very clear on this point: "[These] oaths were given by them of old, who also sought power, which had been handed down even from Cain" (Ether 8:15). Helaman refers to "that same being who did plot with Cain and his followers from that time forth. Behold, it is [Satan] who is the author of [these] works of darkness and doth hand down plots, and oaths, and covenants, and plans of awful wickedness, from generation to generation" (Helaman 6:27, 30).
The book of Moses in The Pearl of Great Price explains something about the secret pacts which Cain and Lamech (a great-great-great grandson) made with the Evil One on separate occasions.
And Satan said unto Cain: Swear unto me by thy throat, and if thou tell it thou shalt die. And swear thy brethren by their heads, and by the living God, that they tell it not. For if they tell it, they shall surely die. And this that their father [Adam] may not know it. And Satan swear unto Cain that he would do according to his commands. And all these things were done in secret. And Cain said: Truly I am Mahan, the master of this great secret, that I may murder and get gain. Wherefore Cain was called Master Mahan, and he gloried in his wickedness. (Moses 5:29-31)
For Lamech having entered into a covenant with Satan, after the manner of Cain, wherein he [also] became [a] Master Mahan [or] master of that great secret which was administered unto Cain by Satan. And Irad, the son of Enoch, having known their secret, began to reveal it unto the sons of Adam. Wherefore Lamech, being angry, slew him, not like unto Cain, his brother Abel, for the sake of getting gain, but he slew him for the oath's sake. For, from the days of Cain, there was a secret combination, and their works were in the dark, and they knew every man his brother. Wherefore the Lord cursed Lamech, and his house, and all them that had covenanted with Satan, for they kept not the commandments of God, and it displeased God, and he ministered not unto them, and their works were abominations, and began to spread among all the sons of men. (Moses 5:49-52)
[John Heinerman, Hidden Treasures of Ancient American Cultures, pp. 62-63]