And the crowd that went in front of him, and those who followed after, were crying out, saying, “Hosannaa to the Son of David! Blessed is he who comes in the name of the Lord!b Hosanna in the highest!” Bible see other translations
“Hosanna” originally meant “Save” or “Save now,” but by NT times it was used liturgically as an expression of praise.
From Ps. 118:26

“Hosanna.” The people who were shouting praises to Jesus as he entered Jerusalem were for the most part not the same group as the group that shouted, “Crucify him” only a few days later. See commentary on Luke 23:21.

“Son of David.” A messianic title. At this point, these people assumed and asserted that Jesus was the Messiah and the true king of Israel (John 12:13) and the Messiah, the “Son of David,” (see commentary on Matthew 1:1). They apparently changed their minds very quickly when he was arrested and beaten.

“the Lord.” For more information on “the Lord” see commentary on Matthew 3:3.

Commentary for: Matthew 21:9