And I believe what I believe is what makes me who I am. I did not make it, no it is making me. It is the very truth of God and not the invention of any man.--Rich Mullins, from the song Creed
Rich Mullins knew what he was talking about with the lyrics posted above. While he was speaking of the Apostles' Creed, I believe what he ways really applies to the whole of liturgy.
Liturgy plays an important role in our worship in many ways, but I think that the most important is how it forms us into "better" believers. Everything that I have said before danced around this notion. Liturgy gets into us, it is habitual and repetitious, it teaches us theology and practical prayers for life. All of these things are formation. Liturgy forms us into who we need to be.