Matthew 24:38-39 "For as in the days before the flood, they were eating and drinking, marrying and giving in marriage, until the day that Noah entered the ark, 39 and did not know until the flood came and took them all away, so also will the coming of the Son of Man be."
Matt. 24:38-39 The Message Bible The Arrival of the Son of Man will take place in times like Noah's. Before the great flood everyone was carrying on as usual, having a good time right up to the day Noah boarded the ark. They knew nothing until the flood hit and swept everything away."
Jesus is prophesying that when He returns it will be just as in Noah's day, people will be dominated with the temporary affairs of this life, their normal every day, eating and sleeping, going to work lifestyle; instead of eternal spiritual truths. Before His return, there will be plenty of signs to show that the time is drawing near, but few will heed them. Preoccupation with the affairs of this life can dull people to the spiritual realities. The Lord kindly, but seriously points out the urgent need to be ready for His return. In the same way that a thief comes when people are the least prepared, so our Lord will return in a time when people are not looking for or expecting Him.
This is not because our Lord desires to surprise everyone and see how many He can catch unprepared. On the contrary, He is urging us to be watchful so that we will be prepared. Jesus gave us the signs of the end times to help us be prepared. He is simply prophesying that there will be a condition of apathy in the latter days that will tend to lull even the faithful to sleep if they don't take heed to His words.
Believers will not be assembled on a mountaintop somewhere waiting for the Lord's return. They will still be going about their daily routines.
In Luke 19:13 The Lord told us in the Church to, "Occupy till I come."
We should be ready for the Lord to come back at any moment, yet work as if His return was still far off.