When Nephi's brethren were about to return to their father after Laman's failed attempt to retrieve the plates of brass, Nephi spoke unto them with an oath: "As the Lord liveth, and as we live, we will not go down unto our father in the wilderness until we have accomplished the thing which the Lord hath commanded us" (1 Nephi 3:15).
According to Brant Gardner, it is very likely that Nephi's brethren knew nothing at this time about Nephi's past vision, and the promise to Nephi that he would rule over them. It is also quite unlikely that the brothers knew of Nephi's impassioned vow to Lehi that he knew that the Lord would prepare the way for them. Nephi's oath ("As the Lord liveth, and as we live") was a powerful commitment. Smith's Bible Dictionary presents the following information on oath-taking:
The principle on which an oath is held to be binding is incidentally laid down in Hebrews 6:16 as an ultimate appeal to divine authority to ratify an assertion. There the Almighty is represented as promising or denouncing with an oath, i.e. doing so in the most positive and solemn manner. On the same principle, that oath has always been held most binding which appealed to the highest authority, both as regards individuals and communities. As a consequence of this principle, appeals to God's name on the one hand, and to heathen deities on the other, are treated in scripture as tests of allegiance. ("Oath," in Smith's Bible Dictionary. Fleming H. Revell Company, 1970, p. 462)
Thus by invoking the name of the Lord, Nephi is binding himself with the strongest of oaths. His subsequent arguments serve to convince his brethren to accompany him. There is no record that the brothers repeated the oath, even though they did participate one more time. [Brant Gardner, "Brant Gardner's Page, "[http://www.highfiber.com/~nahualli/LDStopics/1] Nephi/1 Nephi3.htm, pp. 8-9]
Note* Notice how Nephi is willing to give all he possesses, the very finest (symbolically represented by gold and silver) in order to keep his covenant with the Lord. Notice also how here in 1 Nephi 3:15 he repeats phrasing similar to that of 1 Nephi 3:7 in his covenant oath: "until we have accomplished the thing which the Lord hath commanded". Perhaps that original phrasing in 1 Nephi 3:7 was covenant related to begin with (see 1 Nephi 2:16-24). [Alan C. Miner, Personal Notes]