I thought this passage from the article “Revelation and Promise,” by 20th century Romanian theologian Dumitru Staniloae, was appropriate for Advent. (If you have to read it two or three times before you get it, don’t worry – everyone has that experience when reading Staniloae.)
The acts of the Old Testament revelation prepare and condition the act of the coming of Christ, and this in turn crowns the former. The acts of the Old Testament revelation lay history open for Christ who descends and enters into it. They constitute all the different preparations for the realization of the promise of a Messiah to come. They constitute that history which prepares for the entry into history of one who himself transcends all history. They succeed one another on the path leading towards the gleam of that heavenly light which shone when God came to dwell among men and history was fulfilled by what lies beyond it.