From: Mark 13:33-37
The Time of the Destruction of Jerusalem (Continuation)
(Jesus said to His disciples,)  "Take heed, watch and pray; for you do not know when the time will come.  It is like a man going on a journey, when he leaves home and puts his servants in charge, each with his work, and commands the doorkeeper to be on the watch.  Watch therefore--for you do not know when the master of the house will come, in the evening, or at midnight, or at cockcrow, or in the morning-- lest he come suddenly and find you asleep.  And what I say to you I say to all: Watch."
33-37. "Watch": since we do not know when the Lord will come, we must be prepared. Vigilance is, above all, love. A person who loves keeps the commandments and looks forward to Christ's return; for life is a period of hope and waiting. It is the way towards our encounter with Christ the Lord. the first Christians often tenderly repeated the aspiration: "Come, Lord Jesus" (1 Cor 16:22; Rev 22:20). By expressing their faith and charity in this way, those Christians found the interior strength and optimism necessary for fulfilling their family and social duties, and interiorly detached themselves from earthly goods, with the self-mastery that came from hope of eternal life.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.