1 Thessalonians 5:16

Here we have divers short exhortations, that will not burden our memories, but will be of great use to direct the motions of our hearts and lives; for the duties are of great importance, and we may observe how they are connected together, and have a dependence upon one another. 1. Rejoice evermore, Th1 5:16. This must be understood of spiritual joy; for we must rejoice in our creature-comforts as if we rejoiced not, and must not expect to live many years, and rejoice in them all; but, if we do rejoice in God, we may do that evermore. In him our joy will be full; and it is our fault if we have not a continual feast. If we are sorrowful upon any worldly account, yet still we may always rejoice, Co2 6:10. Note, A religious life is a pleasant life, it is a life of constant joy. 2. Pray without ceasing, Th1 5:17. Note, The way to rejoice evermore is to pray without ceasing. We should rejoice more if we prayed more. We should keep up stated times for prayer, and continue instant in prayer. We should pray always, and not faint: pray without weariness, and continue in prayer, till we come to that world where prayer shall be swallowed up in praise. The meaning is not that men should do nothing but pray, but that nothing else we do should hinder prayer in its proper season.

— Matthew Henry's Concise Commentary (public domain)

In order to "rejoice evermore," we must "pray without ceasing" (Th1 5:17). He who is wont to thank God for all things as happening for the best, will have continuous joy [THEOPHYLACT]. Eph 6:18; Phi 4:4, Phi 4:6, "Rejoice in the Lord . . . by prayer and supplication with thanksgiving"; Rom 14:17, "in the Holy Ghost"; Rom 12:12, "in hope"; Act 5:41, "in being counted worthy to suffer shame for Christ's name"; Jam 1:2, in falling "into divers temptations."

— Jamieson-Fausset-Brown Commentary (public domain)