In 1 Nephi 4 we see the immediate impact of the oath made with Zoram. Hugh Nibley explains why this is significant:
What astonishes the western reader is the miraculous effect of Nephi’s oath on Zoram, who upon hearing a few conventional words promptly becomes tractable, while as for the brothers, as soon as Zoram “made an oath unto us that he would tarry with us from that time forth . . . our fears did cease concerning him” (1 Nephi 4:35,37).
The reactions of both parties make sense when one realizes that the oath is the one thing that is most sacred and inviolable among the desert people and their descendants: “Hardly will an Arab break this oath, even if his life be in jeopardy,”9 for “there is nothing stronger, and nothing more sacred than the oath among the nomads,”10 and even the city Arabs, if it be exacted under special conditions. “The taking of an oath is a holy thing with the Bedouins,” says one authority. “Wo to him who swears falsely; his social standing will be damaged and his reputation ruined. No one will receive his testimony, even if it is true, and he must also pay a money fine.”
But not every oath will do. To be most binding and solemn an oath should be by the life of something, even if it be but a blade of grass. The only oath more awful than that “by my life” or (less commonly) “by the life of my head” is the wa hayat Allah, “by the life of God” or “as the Lord liveth,” the exact Arabic equivalent of the ancient Hebrew hai Elohim. Today it is glibly employed by the city riffraff, but anciently it was an awful thing, as it still is among the desert people. “I confirmed my answer in the Bedouin wise,” says Doughty. “By his life . . . he said, . . . ‘Well, swear By the life of Ullah’ (God)! . . . I answered . . . and thus even the nomads use, in a greater occasion, but they say, By the life of thee, in a little matter.” Among both Arabs and Jews, says Rosenblatt, “an oath without God’s name is no oath,” while “in both Jewish and Mohammedan sources oaths by ‘the life of God’ are frequent.”
So we see that the only way that Nephi could possibly have pacified the struggling Zoram in an instant was to utter the one oath that no man would dream of breaking, the most solemn of all oaths to the Semite: “As the Lord liveth, and as I live” (1 Nephi 4:32).– Hugh W. Nibley, An Approach to the Book of Mormon, 3rd edition, (Vol. 6 of the Collected Works of Hugh Nibley), edited by John W. Welch, (Salt Lake City, Utah : Deseret Book Company ; Provo, Utah : Foundation for Ancient Research and Mormon Studies, 1988), Chapter 10
How would Joseph Smith know about the importance of this specific type of oath?