16 Rejoice always,
17 pray without ceasing,
18 in everything give thanks; for this is the will of God in Christ Jesus for you.
rejoice (v.16) = from Greek xairo, which is from xar = favorably disposed, leaning towards — the word is closely linked to the word for grace, xaris — so the sense here is to consciously delight in God’s grace (Philippians 4:4)
always (v.16) — independent of circumstances
pray (v.17) = from prós, “towards, exchange” and euxomai, “to wish, pray” — properly, to exchange wishes
without ceasing (v.17) = the Greek word is used for a hacking cough — constantly occurring, as in 1 Thessalonians 1:2-3.
give thanks (v.18) = eucharisteo, to give thanks with delight, from charis, that which gives pleasure or delight — We should delight with gratitude to let Him have His way with us “in everything.” This is His will “in Christ Jesus” concerning us. And, remember, it was “in Christ Jesus” that His whole great plan of salvation centered. Thus as He delights in us — charis is the very word for “grace” — we should gratefully delight in His delight of us — mutual delight! And this should be so no matter what the circumstances, for what we have and are in Christ does not change. — Stam, page 101.
in everything (v.18) — in any circumstance
for this (v.18) — referring to rejoicing, praying without ceasing and giving thanks in all circumstances
the will of God (v.18) — as in 1 Thessalonians 4:3, God has informed us clearly what His will for us is
Christ Jesus (v.18) — In Paul’s letters the order is always in harmony with the context. Thus “Christ Jesus” describes the Exalted One who emptied Himself and testifies to His pre-existence; “Jesus Christ” describes the despised and rejected One Who was afterwards glorified and testifies to His resurrection. “Christ Jesus” suggests His grace, “Jesus Christ” suggests His glory. — Vine, page 19
for you (v.18) = into you — the preposition expresses not merely the fact that God desires these things in His children, but also that what is thus taught may be made effectual in them by His power. — Vine, page 90.