Isaiah 64.1-9; 1 Corinthians 1.3-9; Mark 13.24-end

Almighty God, give us grace to cast away the works of darkness and to put on the armour of light, now in the time of this mortal life, in which your Son Jesus Christ came to us in great humility; that on the last day, when he shall come again in his glorious majesty to judge the living and the dead, we may rise to the life immortal; through him who is alive and reigns with you, in the unity of the Holy Spirit, one God, now and for ever. Amen.

ADVENT, it is sometimes said, is a penitential season with subtle shadings of joy, and the frameworks that have given themes to its Sundays both exploit the richly dramatic interweaving of these two strands. Current provisions take us from the Patriarchs and Prophets to John the Baptist and Mary, the exemplary human beings with whom God keeps faith until he appears as the promised Messiah in Jesus. An older scheme confronted the Second Coming more directly, taking worshippers through the four last things: death, judgement, heaven, and hell.

Whatever the balance in our Christmas preparations between joy and terror, the message of Advent is consistent: "Keep watch. . . . Keep awake." The warning to be vigilant comes three times in quick succession in Mark's description of Jesus's bracing his disciples for the coming of the Son of Man (13.24-end). There is no clue to the timing: the only certainty is that, before this event takes place, the Temple that Peter, James, John, and Andrew (13.3) have just been admiring will be destroyed, and that suffering, atrocities, and persecution will follow.

It cannot be a literary accident that, in the very next chapter, Peter, James, and John will be found sleeping three times in Gethsemane, when Jesus has been depending on them to keep watch with him as he wrestles with the prospect of death. Either they have failed to see imminent danger in their preoccupation with events further ahead, or sheer emotional exhaustion has overcome them.

No wonder Jesus has to resort to the obvious when he wakes them the third time with the words "The hour has come. The Son of Man is betrayed into the hands of sinners" (14.41). Did they spend the rest of their lives wishing that they could have had that hour back to keep awake and keep faith with Jesus? All of them would go on to keep faith, three of them (including Andrew, whose feast day is transferred to 1 December this year) meeting violent deaths. But this lost opportunity must have left its mark.

Having another chance is not, however, always the answer - or, at least, not the whole answer. The third part of the prophecy of Isaiah dramatises a dialogue between God and the people whose parents and grandparents may have seen the First Temple destroyed before they were taken into exile (63.1-64.11). Back in their own country, they long for God's return in demonstrations of power to be present and active among them, but need to learn that their own sin has fractured the relationship.

God has hidden his face, withdrawing the gaze of approval (Genesis 1.31) which guarantees life itself (Psalm 104.29). What is left to hope for? Only the wager that God remains constant, even when God's creatures do not; that the potter will not disown the clay he has moulded, and may even be prepared to start again, remoulding it in a purer and more beautiful form (64.8).

The prophet yearns for the restoration of a rhythm of faithfulness: God's call, human response; God's strengthening presence through periods of waiting; human faithfulness in holding to the promise of God's presence. This is what Paul wants the Corinthian Church to understand. No one knows when "the day of our Lord Jesus Christ" will come, but it will come. They are to live now as those called into his fellowship, while keeping awake to meet him when he appears.

The collect, one of Cranmer's own compositions (modernised), responding to the Advent Sunday Epistle in the Prayer Book lectionary (Romans 13.8-14), urges us also to practise "in the time of this mortal life" for the time when Christ will "come in his glorious majesty to judge the living and dead".

Our information about this coming is just as mysterious as that available to the disciples and the Corinthian Church. In the time between, we must learn to be watching people, watching with those driven from their homelands by war and invasion, the families of hostages, the medical teams and volunteers keeping vigil with patients with the Ebola virus, and the ordinary everyday sufferers around us. Advent teaches us the accents of waiting - anguish and self-examination often, but always hope and joy in a faithful God.

The Revd Rosalind Brown has come to the end of her commentaries on the three-year lectionary cycle. A new writer starts this week.

Dr Bridget Nichols is Lay Chaplain and Research Assistant to the Bishop of Ely, the Rt Revd Stephen Conway. She grew up in South Africa, in one of the former gold-mining towns east of Johannesburg, and attended university in Cape Town, to study English and Classics. She returned to Johannesburg, and completed an MA in English at Witwatersrand University. She then travelled to England, and came to the Centre for the Study of Literature, Theology and the Arts, at the University of Durham, with a plan to write on Prayer Book collects. The subject expanded, and her doctoral research was published as Liturgical Hermeneutics: Interpreting liturgical rites in performance (Peter Lang, 1996).

She is also the author of Liturgy in Christian Perspective (DLT, 2000), and edited and contributed to The Collect in the Churches of the Reformation (SCM, 2010).

She acts as Reviews Editor for the Society for Liturgical Study's journal, Anaphora. Since 2011, she has been a member of the Liturgical Commission, and, since 2012, a member of the Academic Board of the Archbishop's Examination in Theology.