In essence, these verses are Christ's opening salvo on how to be prepared and how to use your time and energy when the evidence of His return begins to appear.
Although we definitely know that we are living in the time of the end, we do not know exactly when Christ will return. So we have to live in readiness every day. The theme of this brief parable is expectation. Knowing the general signs of His coming, we live expecting the unexpected.
He illustrates this by comparing His coming to that of a thief. We normally do not look for thieves. Understandably, thieves do not advertise their coming, but by taking precautions, we prepare against their coming. All of us lock our houses and hide our valuables in safe places. Some of us have installed security alarms and exterior lighting to discourage burglary.
In the same vein, Jesus urges His people to be vigilant, alert, wakeful, and constantly watchful because a thief's principal weapon is surprise. Even to those who are aware, His coming will occur with jarring suddenness—and more so to those who are distracted by ordinary occupations, "eating and drinking, marrying and giving in marriage." The teaching in this parable is that to live without vigilance is to invite disaster.