Once Christ identified himself to everyone "one by one" (3 Nephi 11:15), the people "did cry out with one accord, saying: Hosanna! Blessed be the name of the Most High God!" In Hebrew, Hosannah means "save now." This phrase is somewhat puzzling to many biblical scholars. It has been alternatively interpreted as an intercessory prayer, asking that the Lord might now send salvation; asking for assistance, that it be given to the Messiah. It has also been understood as some kind of royal supplication addressed to the Messiah, or perhaps a call of triumphant joy. Whatever it was, we know that the phrase Hosannah had great Messianic significance, and that it was associated with the anticipated coming of the Messiah, with the cleansing of the temple, and was certainly at home in Israelite temple ritual.
The Hallel, an ancient festival hymn which was a part of Israelite temple liturgy, reads "Hosannah. Save now, I beseech thee, O Lord: O Lord, I beseech thee, and now prosperity. Blessed be he that cometh in the name of the Lord: we have blessed you out of the house of the Lord." (Psalms 118:25-26). This was certainly well known in Israel, so it is significant, I think, that in this temple context at the temple in Bountiful all of these Nephites broke forth, crying out in unison spontaneously with this familiar liturgical temple expression. [John W. Welch, "Christ at the Nephite Temple," in Teachings of the Book of Mormon, Semester 4, p. 134]