For you yourselves know perfectly that the day of the Lord so comes as a thief in the night. 1 Thessalonians 5:2
In the Scriptures, the exhortation to prepare for the day of the Lord is usually given to God’s people, rather than to unbelievers. Christians must be prepared for Christ’s return, so that they can properly respond to Him. The most important thing about the day of the Lord is clear: it comes unexpectedly.
In Scripture, there are several references to the day of the Lord. Often this refers to Jesus’ first coming or His second coming, but it can also refer to any time God comes to His people, either in salvation or judgment (Isa. 13:6; Joel 2:11; Mal. 3:2). Amos had predicted that the day of the Lord would be far different from what the people expected (Amos 5:18). The people of his day thought it would come with joy and singing, yet Amos said there would be grieving and judgment of sin. When Jesus came the first time, His coming caught people by surprise. Because they were expecting the Messiah to come in a different way, many did not recognize Him.
The final day of the Lord will be at Christ’s second coming. Meanwhile, there will be times when God will come to you, your family, and friends. You need to be watching for the signs of God’s convicting work in your children, your friends, and your coworkers. You must take notice when God begins to do a special work in the lives of the people in your church. It may be that you have an unusual sense of God’s presence in a worship service and you begin to intercede for those who are present. Prepare yourself now and pay attention to what is happening in the lives of those around you. You may discover that the day of the Lord is at hand.