Matthew 21:9 Then the multitudes who went before and those who followed cried out, saying: “Hosanna to the Son of David! ‘Blessed is He who comes in the name of the LORD!’ Hosanna in the highest!”
Hosanna-(interjection)-an exclamation, originally an appeal to God for deliverance, used in praise of God or Christ.
The people were praising Jesus by shouting praises to Him! Just think, less than a week later, He would be on a cross, dying for the sins of the entire world! Thank you Jesus!