First reading( Isaiah 63:16-17, 19; 64:2-7) explained:Around 600 BC, the Babylonians took the Jews out of the Promised Land and kept them in exile (the Babylonian Captivity) for about 60 years.  When Cyrus, the Persian emperor, took over Babylon, he sent the Jews home.  This reading is set in that troubled period when Judah was trying to put itself back together after returning from Exile. 

To get the flavor of it, imagine how a contemporary family might feel when they return to a fire-damaged. or hurricane-destroyed, or flood-damaged home.  The reading contains a mix of feelings: guilt, and outrage at God, alternating with praise of God, humility, anguish, and hope. 

Isaiah expressed the hope of Israel for a powerful manifestation of God in their midst.  "Oh, that You would rend the heavens and come down, with the mountains quaking before You.”  The prophet hoped that if God would come into their midst, the people could be faithful to Him.

Acknowledging the fact that the people were unfaithful, Isaiah asked for God’s forgiveness and acceptance: "You, O Lord, are our Father; we are the clay and You are the potter: we are all the work of Your hands."  In other words, we're not perfect, but we are totally God’s to shape. 

Here Isaiah was not anticipating Jesus’ arrival when he asked God “... to rend the heavens and come down ...”!  He was simply pleading with Yahweh to force those Israelites who had recently returned from the Babylonian Exile to do what was necessary to allow God to be present and active in their lives. 

Isaiah was praying to Yahweh on behalf of the Israelites, “Would that You might meet us doing right, that we were mindful of You in our ways!”  He begged Yahweh, the Father of the Chosen People, for mercy.  This prayer was answered when the Son of God became man in the Incarnation.

Second Reading (1 Corinthians 1:3-9) explained:We wait for Christ in two ways. The early Sundays of Advent teach the end-of-the-world theme. In this context, we wait for Christ to “come again in glory, to judge the living and the dead.”  The later Sundays of Advent celebrate a different theme: the coming of the Messiah in the flesh.

Today’s second reading, taken from the first letter of St. Paul to the Corinthians and written from Ephesus in 57 A.D., begins with a greeting and a thanksgiving prayer. The letter is Paul's answer to reports which had reached him concerning disputes and difficulties in Corinth. It was written while he and his audience were still sure that Christ's second coming was just around the corner.

Like all early Christians, the Apostle used the phrase “the Day of our Lord Jesus Christ” as another way to speak about Jesus’ Parousia — his Second Coming at the end of the world. Paul reminded the Corinthians that they were not ready to face the Day of the Lord because they were misusing the gifts of the Holy Spirit. After describing the special gifts of the Holy Spirit  they had received, Paul reminded the Corinthians that they were using their gifts in the wrong way.

Christ's favor, the speech and knowledge they possessed, the spiritual gifts in which they gloried -- all were useless unless used for the good of the community. In fact, many of Paul's converts had been using their gifts to destroy the community instead of building it up. What should have been an asset, had become a detriment.

Paul could only pray for the eventual conversion of his community. "He (Jesus) will strengthen you to the end," the Apostle writes, "so that you will be blameless on the day of Lord Jesus Christ. God is faithful, and it was He who called you to fellowship with His Son, Jesus Christ our Lord."

Today’s Gospel is the conclusion of a speech found in Mark 13, in which Jesus foretells his Second Coming (Parousia), at the end of time or at the end of the world.  Ten years after Paul’s death, Mark reminded his community in Rome of Jesus’ words, “Be constantly on the watch! Stay awake! You do not know when the appointed time will come.” The evangelist knew that if an expected event didn’t happen as quickly as expected, people would stop doing the things they ought to do. 

Hence, Mark reminded them of Jesus’ parable about the gate-keeper in the house of a traveling master. Since the master was traveling, his servant must be constantly alert, “at dusk, at midnight, when the cock crows, or at early dawn.” There was always a fear that the master would come home “suddenly and catch you asleep.” In such situations, one must constantly, “be on guard!” When Paul and Mark spoke about the things to come, it was only to remind their readers that their present behavior wasn’t measuring up to what Christ’s second coming demanded.

Gospel exegesis:The context:Mark is the shortest of the four canonical Gospels and, in the view of most Scripture scholars, was the first of them to be put down in written form, probably sometime in the 60s A.D. The Gospel ofMark was probably written at a time when the Romans had swept through upper Galilee to suppress a Galilean revolution.  This region was where Mark's Judeo-Christian community lived and was besieged by three hostile forces, all of which demanded loyalty from the followers of Jesus as former Jews.  Since Palestine was the breadbasket of the Empire, the Romans controlled it through military might and local alliances.  The high priests and their minions collaborated with the Romans and imposed their own oppressive burden of regulations and Temple taxes.  Armed Jewish nationalists had seized the Temple by force and wanted to expel the Romans from the region.

At the time Mark wrote his Gospel, the Roman legions were poised to destroy the Temple and all of Jerusalem with it, once and for all, and thus end the Jewish nation as it had existed before. Hence, Mark reminded the Christian community of Jesus’ injunction to be alert and awake for Christ’s second coming, recalling Jesus’ parable about the gate-keeper. Scripture scholars sometimes refer to this part of Mark’s Gospel as the “little apocalypse” because these verses speak of the striking cosmic signs that will signal Christ’s coming (vv. 24-27), and Christ’s injunction to be watchful and attentive (vv. 28-31). 

The background of the parable: Absentee land-owners and wayfaring masters were a common thing in Jesus' time. The owners of large properties often lived elsewhere, leaving servants in charge of caring for their properties and carrying on business as if the owners were still present. This kind of situation would be a test for the servants left in charge. Would they be faithful day by day, or would they wait until they heard the master was about to return and then quickly get things in order? The trouble was that often they didn’t know when the land-owner would return. The absence of the master was a test. 

The need for Christian alertness: Jesus illustrates the need for alertness and readiness by comparing the situation of his followers to that of a gate-keeper in a house when the owner was out of the country.  Since the gate-keeper did not know when the owner of the house would return, "in the evening, or at midnight, or at cockcrow, or in the morning," he must always be ready, if he did not want the owner to find him asleep.  In the same way, there is no reason for Christ's followers to be fearful, provided we are ready every day for Jesus' return.  If we are awake and ready, the coming of the Son of Man is an event to be greeted with joy. Thus, our whole life should be a preparation to meet the Master. We base this constant watch not on fear but on hope in God’s promise of eternal life .

The work to be completed: Like the parents who trust their teenagers to look after the house while they are away, or like the teacher who leaves the classroom after giving her students plenty of work to do, Jesus trusts us to carry out his work until he returns. There is the work of witnessing to Jesus in our daily lives. There is the work to be done in our families, our schools, our local churches and our community. There is the work of caring for those who are hurting and have needs.  There is the work of guiding and leading others, pointing people to the comforting message of the Gospel. Always, there is the work of living "lives holy and dedicated to God,” and so “doing our best to be pure and faultless in God's sight and to be at peace with Him"

Being a responsible servant: This passage reminds us also that we should not be so foolish as to forget God and become immersed in worldly matters. Using Christ’s parable, the Church reminds us of the alertness and preparation needed for the four-fold coming of Jesus into our lives, namely: at the celebration of His Incarnation during this Christmas season, in His active presence in our daily lives, at the moment of our death, and in his final coming in glory at the end of the world. 

First coming and second coming (St. Cyril of Jerusalem): At the first coming he was wrapped in swaddling clothes in a manger. At his second coming he will be clothed in light as in a garment. In the first coming he endured the cross, despising the shame; in the second coming he will be in glory, escorted by an army of angels. We look, then, beyond the first coming and await the second. At the first coming we said: “Blessed is he who comes in the name of the Lord!” At the second we shall say it again; we shall go out with the angels to meet the Lord and cry out in adoration: “’Blessed is he who comes in the name of the Lord!’. … His first coming was to fulfil his plan of love, to teach us by gentle persuasion. This time, whether people like it or not, they will be subjects of his kingdom, by necessity.” (St. Cyril of Jerusalem; transl. http://www.universalis.com)