In the Old Testament 'Hosanna' is used as a cry for help, as a desperate plea and as a cry for God to save his people. The kind of cry you would shout when you are drowning and can't swim. It's used like that in Psalm 118.25
However, in the New Testament the meaning of the word Hosanna changes. It is used more as a shout of hope and praise and exultation. It's used when Jesus comes riding into Jerusalem on the donkey. Rather than meaning "Help, save us"... it now means "Our Salvation has come! Hooray!" The reason for this is because Jesus has now come. Rather than crying out desperately for a redeemer, we can cry out confidently because our redeemer has come. 'Hosanna' switched from being a plea to praise.
I particularly like this because Hosanna is my middle name and i can deeply identify with both it's meanings. I remember when all my heart could do was desperately cry out "Help" and "Save your people", but i know too what it is to be able to freely and confidently rejoice that the answer to my cry has come, in the form of Jesus.
I remember clearly when my own cry of Hosanna kinda changed..... from being a desperate cry, to being a confident cry. From being hopeless to hopeful. The difference between when you are drowning and you can't see any-one around to help, and when you are drowning but you can see the life-guard jumping in to save you - you may still cry 'help' but this time you know you will be alright.
Last night i had that same revelation again... i realised that this last week i had been crying out "Hosanna" in the Old Testament way... in desperation.... and had been slightly losing sight of the freedom and victory and hope and confidence we do have in God. Anyway, out of no-where, i was suddenly reminded of this as i was going to sleep yesterday and was filled with such sweet joy again. That was much needed.