16 Rejoice always,
17 pray without ceasing,
18 give thanks in all circumstances; for this is the will of God in Christ Jesus for you.
These three verses are to be read as one unified statement.
Nowhere is worship made manifest more than in prayer. Prayer according to His will, i.e. Word (1 John 5:14-15) is as much, if not more so, an expression of our worship/obedience, as singing a song, or lifting hands.
The will of God is that we offer joyful, grateful prayer always, in every circumstance; as even the circumstances are His will. The circumstances, as determined by God, provoke such prayer (Psalms 107:23-32)
Romans 8:28 And we know that for those who love God all things work together for good, for those who are called according to his purpose.