The purpose of Advent is to help us prepare for Christmas. One can’t understand the message of Christmas unless we are familiar with at least the broad outlines of the history of salvation.
The Advent Liturgy relives in a microcosmic way the history of Israel, viewing it through the eyes of Christian faith. It shows that all of that history was pointing and leading toward Jesus. He was the one who fulfilled the messianic prophecies.
Advent takes us back in time so that we may appreciate the greatness of what we are heirs to: We are the heirs to the promises God made to the prophets. Advent helps us to appreciate the great blessings God has given us in Christ.