the wiki article is really good
https://en.wikipedia.org/wiki/Advent
I thought it might be the usual marxist crap in the lines of - "Christians believe, and quite honestly I have no idea why....."
but instead it is written by a Christian - cleric and theologian and draws parallels with the birth of Christ and re-birth of Christ ( resurrection ) . And it draws parallels with other Christian traditions ( some churches believe Christ was always God ( monophysite) and some only ever human (unitarian). I hesistate to mention it on AB