I wrote earlier about the way the Gospel for the first Sunday of Advent seems to undercut its setting. On the fourth Sunday of Advent, something similar (and different) occurs. Much of the Gospel (Matthew 1:18-25) attends to St. Joseph:
This is how the birth of Jesus the Messiah came about: His mother Mary was pledged to be married to Joseph, but before they came together, she was found to be pregnant through the Holy Spirit. Because Joseph her husband was faithful to the law, and yet did not want to expose her to public disgrace, he had in mind to divorce her quietly. But after he had considered this, an angel of the Lord appeared to him in a dream and said, “Joseph son of David, do not be afraid to take Mary home as your wife, because what is conceived in her is from the Holy Spirit. She will give birth to a son, and you are to give him the name Jesus, because he will save his people from their sins.” All this took place to fulfill what the Lord had said through the prophet: “The virgin will conceive and give birth to a son, and they will call him Immanuel” (which means “God with us”). When Joseph woke up, he did what the angel of the Lord had commanded him and took Mary home as his wife. But he did not consummate their marriage until she gave birth to a son. And he gave him the name Jesus.Joseph and Mary are bound by marriage (the text is usually translated with some reference to "engagement" but the culture at the time considered an engaged couple "married," for legal purposes, even though the ceremony was in the future); the Law permits Joseph to call for a public tribunal inquiry into whether Mary has become pregnant as a result of a liaison she entered into willingly, or whether she was forced. Joseph's decision to forego all such investigation shows him to be a man who is not simply observant of the Law but fully attuned to its spirit; he does not insist on his rights, he does not bank on the privilege his position gives him; he is ready to do everything he feels called upon to do. It is after this readiness that his dream says to him: something further, something orthagonal to the Law, is transpiring. And yet in it, both the law and the prophets are fulfilled. It is via Joseph that Jesus' connection to the Davidic promise derives; Joseph is Jesus' father in the eyes of the Law by virtue of having named Him. Modern commentators worry over the words that get rendered as "virgin," the Masoretic text's almah (strictly speaking this is inexact; lexicographers assure us that the word more precisely means "young woman") and the LXX's (accurate) parthenos, but Matthew is not concerned with these. What is all the more striking is that Matthew provides the explicit gloss on "Emmanuel," and an implicit one on "Jesus", i.e., "Joshua", but he passes over in silence the obvious fact that these names are not the same name -- this despite his presenting the one narrative as the fulfillment of the other.
So the Law is thus not abrogated, but its fulfillment in letter and spirit point beyond it, to something strange and new. And prophecy is presented as fulfilled in a manner that clearly is not "literal" (it is precisely the letter which is not fulfilled), but in such a way that the writer does not bat an eye at any discrepancy.
The first Sunday of Advent, the reading (in the liturgical context of the beginning of the Year): you cannot measure time accurately, you cannot know the times. It is about the future exceeding the present. The fourth Sunday of Advent, the Gospel is about the present exceeding the past. This puts the matter far too schematically; the point however is that whatever scheme we have in place is fulfilled precisely in being shown to fail as too schematic.