Therefore we are called to be vigilant because we do not know the 'precise moment' when the master will return to the house. The 'house' can be seen as an image of the Christian community which prepares itself with vigilance through prayer and works, to welcome the master. The 'house' can also be thought of as the spiritual dwelling of each of us that needs to be built daily.
Everyone must also take care to complete the work that God has entrusted to them, watching that they will not find themselves unprepared for the Lord when he comes. The season of Advent calls us to strengthen our spirit of prayer, carefully fighting the negligence and the weakness that makes us yield to sin.
Blessed John Henry Newman wrote in his spiritual diary that to be vigilant with Christ is to look ahead without forgetting the past. It is not to forget that He has suffered for us, it is to lose ourselves in contemplation of the grandeur of redemption. It is to continually renew the passion and agony of Christ - to cover with joy that mantle of affliction that Christ wore first and then left behind when he ascended into heaven. It is separation from this sensible world to join the life beyond the senses. This is how Christ will come, and come in the way he has said. (J. H. Newman, Diario spirituale e meditazione, 93).
Excerpts of a Letter for the First Sunday of Advent from the Congregation of Clergy