For just as the days of Noah were, so will the coming of the Son of Man be. For as they were in those days before the flood, eating and drinking, marrying and giving in marriage... so also will the coming of the Son of Man be. At that time two men will be in the field; one is taken and one is left. Two women will be grinding at the mill; one is taken and one is left. Watch therefore, for you do not know on what day your Lord comes.... For this reason, you also be ready, because at an hour when you do not expect it, the Son of Man is coming.
Matt. 24:37-44
So warned Jesus concerning the need for His believers to be watchful and ready, that they would not miss His second coming.
In the days of Noah there were two conditions existing: people were befuddled by eating, drinking, marrying and giving in marriage, and they did not know that judgement was coming, until the flood came and took them away. Similarly, at the time that the Lord returns, people will be befuddled and distracted by the necessities of this life, and will not realise that God's judgement (signified by the flood) is coming upon them.
In the beginning, eating, drinking and marriage were ordained by God for man's existence; however, Satan now utilises these necessities to occupy man and keep him from God's interest. Even a glance at the world situation will confirm that man is fully occupied with material things and has no sense of the coming judgement.
However, a small number of His believers will be watchful and sober. The two men and the two women signify believers, living their normal lives. The two men are working in the field - they're not sitting in a Bible study group; the two women are grinding at the mill - they're not fasting or praying in a prayer meeting. However, one of each group is taken by the Lord at His secret coming, that is, raptured before the great tribulation comes. What is so special about the man and woman who are raptured, and why are the other two not?
This is surely a matter of their condition related to life. Those who are taken have matured in life, while those who are left are, spiritually speaking, immature. This means that in our life, we must firstly be diligent in our work, but at the same time, we must take care of our spiritual condition. We cannot give our all to our work and neglect our growth in life; nor can we be super-spiritual and reject the requirement to work for our daily needs. Instead, we must be balanced and normal.