PLEASE HELP ME! Ten points to whoever helps..need the name of an advent song?

There is this song they play on the second and third weeks of advent during the communion procession (I think they do it at every church). The thing is I couldn't hear the words all the clearly. I know in the verses it keeps repeating "teach us" and in the chorus it goes "hossanah" and "messiah". Sorry I didn't give much information, but PLEASE help!!