I did not grow up in a Christian family and so my only connection to Advent was the beloved 'Advent Calendar'. Man, I loved those things. Opening the little doors to discover what lay beneath! But Advent meant no more to me than a countdown to Christmas (and, though I was aware of the story of Jesus' birth, Christmas meant no more to me that good presents, good TV, and good food).
When I became a Christian I quickly migrated into free church charismatic circles and here we 'do' Christmas and we 'do' Easter but we don't 'do' anything else in The Christian Year. So I was always aware when Advent started - we still have Advent Calendars - but I never really 'got' it.
I was amazed to discover a couple of years ago that Advent is not simply a countdown to Christmas but in fact brings together anticipation for the first and the second comings of Jesus. (I can hear all my Anglican and Catholic friends laughing - "Like everyone knows that dude!" Well, I had to hang around academic theologians for over twenty years before I discovered it!)
My initial reaction, after recovering from the news, was to think, "What a mess the Church has made by starting The Christian Year with a confusing mash-up of the first and the second coming of Christ."
But then I started to get the wisdom of it.
Old Testament traditions do not contain a single, unified eschatological vision but different threads of hope that tangle and disentangle in different traditions. Certain motifs crop up again and again in differeing combinations (e.g., the return of Israel from exile to the Land, a coming Davidic Messiah, the defeat of Israel's enemies, a new covenent, the pilgrimage of the nations to Zion to worship Yhwh, the giving of the Spirit, new creation). No single place pulls it all together but the impuslse to synthesize and hold the motifs together somehow or other was strong.
So it was that longing for a better future was woven into the fabric of Second Temple Judaisms (albeit in various different ways).
The surprise of the salvation that Jesus brought was that it fulfills the unified hope of Israel not in a single seriel-act of redemption but in a two-stage event.
Phase 1: Jesus' first coming, his life, death, resurrection, ascension, and the giving of the Spirit ...
Phase 2: Jesus' second coming to bring the work of his first advent to completion.
By holding together the first and second advents the Chruch was not confusing matters but helping worshippers to perceive that we cannot understand either advent apart from the other. The salvation wrought by Christ is a single salvation albeit implements over a long period.