To take a Jewish example, at the Seder (Passover meal) each year a child asks an elder "Why is this night special? What's so special about it, huh?" (I paraphrase.) And the elder replies, "This is the night the Lord brought us out of slavery in Egypt." Now this doesn't mean that the Jews are brought out of slavery each year, but that one of the functions of a liturgical calendar (in Jewish terms other examples would be Purim, and Hanukkah, and the 9th of Av, and... actually most of the holidays, including Pentecost, which has a different historical focus for Christians, just as has Passover itself) for a historically based faith is to recount the history. And in a sense (with some radically different interpretations, sometimes) all Jewish history up to the time of Jesus is Christian history.

Liland