But something happened to that phrase, hoshiya na. The meaning changed over the years. In the psalm it was immediately followed by the exclamation: "Blessed is he who comes in the name of the Lord!" The cry for help, hoshiya na, was answered almost before it came out of the psalmist's mouth. And over the centuries the phrase hoshiya na stopped being a cry for help in the ordinary language of the Jews. Instead it became a shout of hope and exultation. It used to mean, "Save, please!" But gradually it came to mean, "Salvation! Salvation! Salvation has come!" It used to be what you would say when you fell off the diving board. But it came to be what you would say when you see the lifeguard coming to save you! It is the bubbling over of a heart that sees hope and joy and salvation on the way and can't keep it in.
So "Hosanna!" means, "Hooray for salvation! It's coming! It's here! Salvation! Salvation!"
And "Hosanna to the Son of David!" means, "The Son of David is our salvation! Hooray for the king! Salvation belongs to the king!"
BY: John Piper, Piper Notes 1983,1998