When John enters heaven, he stumbles into a worship service. Four living creatures offer praise “day and night without cease” (anapausis), like the saints in 7:15 (like the temple servants in Leviticus 8:35; 1 Chronicles 9:33). 

The Lord exacts ceaseless day-and-night worship later on in the book: Those who worship the beast and his image, who are sealed with his seal, are tormented forever (14:9-12). The Lord pours a libation of wrath over them, and their smoke rises like a continuous offering(v. 10). The same fate awaits the beasts and the dragon (20:10).

Worship appears to be inescapable. Either worship God day and night, or worship beasts and dragons. Either way, the worship will be without cessation.