What does 1 Thessalonians 5:16 mean?

According to this verse, Christians should be joyful at all times. Practicing unconditional forgiveness allows us to obey the command to "rejoice always." A bitter, unforgiving spirit blocks joy as surely as a logjam blocks the flow of a river. Scripture recognizes that our circumstances might not always result in our being "happy," but happiness is not the same thing as joy. Joy, in the Bible, involves a trusting hope in Christ, leading to an eternal perspective (James 1:2–3; Hebrews 12:2).

Paul practiced what he preached. When he wrote to the Philippians from prison, he didn't live under his circumstances, instead he rose above them. Even though he was shackled, he rejoiced in the Lord (Philippians 1:17–18; 4:10). The Thessalonians' circumstances were difficult, but they could be joyful "in the Lord." Paul's joy overpowered his trials. In spite of ill-treatment, brushes with death, sorrow, and virtual poverty, he always rejoiced (2 Corinthians 6:8–10).

Jesus linked joy to obedience. He said, "If you keep my commandments, you will abide in my love…These things I have spoken to you, that my joy may be in you, and that your joy may be full" (John 15:10–11).