From The Encyclopedia of Mormonism
Author: Woodbury, Lael J.
Among Latter-day Saints, the sacred ceremony of the Hosanna Shout is usually reserved for temple dedications. It is given in the spirit of thanksgiving and petition, fulfilling the instruction to bless the name of the Lord with loud voices and "with a sound of rejoicing", with "hosannas to him that sitteth upon the throne forever" (D&C 19:37;36:3;39:19;124:101).
When the ordinance of the washing of feet was introduced at Kirtland, shouts of hosanna were viewed as a sealing benediction on both private and quorum prayer and then on the dedicatory prayer. At prayer meetings in the Kirtland Temple, the Saints sometimes used related phrases such as "Blessed is the name of the Most High God" and "Glory to God in the highest" (HC 2:386).
The Hosanna Shout is whole-souled, given to the full limit of one's strength. The congregation stands and in unison shouts the words "Hosanna, Hosanna, Hosanna to God and the Lamb. Amen, Amen, and Amen," repeating them three times. This is usually accompanied by the rhythmic waving of white handkerchiefs with uplifted hands. The epithet "Lamb" relates to the condescension and Atonement of Jesus Christ.
The Hosanna Shout memorializes the pre-earthly Council in Heaven, as "when all the sons of God shouted for joy" (Job 38:7). It also recalls the hosannas and the waving of palm branches accorded the Messiah as he entered Jerusalem. And hosannas welcomed him as he appeared to the Nephites. President Lorenzo Snow taught that this shout will herald the Messiah when he comes in the glory of the Father (cf. 1 Thes. 4:16).
Woodbury, Lael J. "The Origin and Uses of the Sacred Hosanna Shout." In Sperry Lecture Series. Provo, Utah, 1975.
LAEL J. WOODBURY