A Glimpse of the Apocalypse

The Lord Jesus devoted much of his preaching to warning his followers of the suddenness with which the world would end.  St. Ambrose of Milan comments in his "Exposition of the Seven Visions of the Apocalypse":

" 'Be vigilant and strengthen those who are about to die' (Revelation 3, 2).  The one who is vigilant performs good works.  He is commanded to keep watch by exercising himself in the works of charity, lest he lose the small goods which he seems to have.  Just as a dead body is without a soul, so whatever goods we seem to have are dead if charity be absent.  'For I do not find your works full before my God.'  They were not full but empty because they were not filled with charity.  Such was the case of the five foolish virgins who were sent away from the dwelling of the heavenly Spouse because they did not have the oil of charity in their vessels (cf. Matthew 25, 10-12).  

" 'Have in your mind how you received and heard, and then obey and do penance' (Revelation 3, 3).  That is, remember how you took wholly the faith of Christ in baptism, when you promised to renounce the devil and all his works.  Remember how you heard from the teachers of the Christian faith, who taught you the faith in Christ, how it is necessary for you to live: 'And obey what you have heard and do penance', for you have been useless, regarding good works, for a long time.  'If you do not keep watch', that is, if you do not exercise yourself in the performing of good works, 'I shall come as a thief, at an hour that you do not know.'  The Lord will come to them as a thief in order to take them away through death from this worldly dwelling.  These are those who rest in their depravities and neither wish to abstain from their vices nor set their own death before their eyes.  As The Lord says in the Gospel: 'If the head of the household knew at what hour the thief would come, he would keep awake until then and not let his house be broken into' (Matthew 24, 43).  We can understand the 'head of the household' as the mind: for, just as the head of the household rules his house, so also does the mind govern all the acts of the body as well as all thoughts.  The head of the household 'sleeps' and the thief breaks into his house when the mind rests in carnal pleasures, unforeseen death arrives, it breaks into the 'house' of the body, and draws away the soul.  If he had kept watch, that is, persevering in good works, death would not carry him away as a thief, but as a liberator."