The purpose of a sermon

Our most recent assignment and also the past few readings have made me wonder what exactly the purpose of a sermon is. What do people look a for once a week on Sunday? I used to always think that a sermon was a sort of weekly "spiritual renewal" - a chance to reflect on God in this time taken out of the busy week. But I don't think this was always the case - church on Sunday wasn't always the exception - I think religion used to be a much larger part of Christians' day to day lives. Has the purpose of the sermon shifted since people's relationship to religion has shifted? I think that at one time, the sermon may have been more about teaching than about consolation or renewal.

In any case, how does scripture relate to the purpose of a sermon? What's interesting is that I think scripture can function in a sermon in these different ways and others. Scripture, in this case the Old and New Testaments, encompass so many ideas that it can be used from purposes of teaching to purposes of consolation.