The Second Coming of Christ will affect everybody (Revelation 1:7).  Great joy will come to the believers and the fear of judgement to unbelievers (1 Thessalonians 5:3).  The contrast will be the difference between night and day.  So, all believers should be waiting expectantly, even though the world will be utterly shocked by the unexpected appearance of its Judge.  Therefore Paul urged God's people to wake up, realise their eternally privileged position, and stop living like the people who are away from God.
 

Each follower of Jesus is related to every other believer; they are spiritual brothers and sisters.

Joy is one of the consequences of the Holy Spirit's presence in a believer (Galatians 5:22). It expresses the relief of sins forgiven, the confidence of being loved by God and the prospect of being welcomed by Jesus when He comes again. But adverse circumstances, inner conflicts and doubts may dull our joy.

What is the faithfulness of God, and to whom is He faithful? Faithfulness is part of His character; He never deviates from who He is and He always fulfils what He has promised. He is true to His Word. Because of God's unchanging nature Father, Son and Spirit implicitly trust one another other (Hebrews 3:2).