Be Joyful Always
1 Thessalonians 5:16 (ESV) … “Rejoice Always,”
The great composer, Joseph Haydn, was once asked why his church music was so cheerful. He replied, ‘When I think upon God, my heart is so full of joy that the notes dance and leap, as it were, from my pen, and since God has given me a cheerful heart it will be pardoned me that I serve him with a cheerful spirit.’
A Christian’s joy is not a natural joy that ebbs and flows according to the circumstances that surround us, but a supernatural joy that comes from God and is rooted in our relationship with him. It is a joy that fills our hearts even in the midst of persecution. Joy was one of the marks of primitive Christianity, which amazed the heathen world and attracted men to Christ. Paul is concerned that the joy of the Thessalonians might be strangled by suffering, so he urges them to rejoice not in what was happening to them, but in their Saviour and all that he has done for them. 
 Shenton, T. (2006). Opening up 1 Thessalonians (pp. 108–109). Leominster: Day One Publications.