In his book, The Spirit of the Liturgy, Pope Benedict refers to worship as play. This sounds a little strange at first but when you consider what children are doing when they play it all becomes clearer.
Watch any little boy or girl playing. He has his toy truck, his model aeroplane or his tool set and she has her doll or her teaset, or some other toy. What are they really doing? They are playing at real life, adult life. They are practising for a life which is still to come, which will come when they are adults.
That's what we do at Mass. Aren't we rehearsing for heaven? Aren't we practising for that time which lies in the future, when we all gather for the heavenly banquet, the real Mass?
Playing is an activity of little children, adults move on to more serious things but to those who are too adult to play Mass Jesus might say: Unless you become like little children ....