They serve him day and night in his temple.
In the Old Testament only the priests could enter the temple of God, let alone do the work of service befitting the temple. The cherubim Solomon engraved on all the walls of the temple (1 Kings 6:29; 2 Chronicles 3:7, 2 Chronicles 3:14) recalled the cherubim guarding the way back into the Garden of Eden (Genesis 3:24) and illustrated that the people could not enter the temple of God. But in the heavenly temple John sees, the saints of the New Testament times are free to enter God’s temple themselves. That is because the Lamb of God (John 1:29) has atoned for sin, and so the cherubim‑laced curtain torn from top to bottom (Mark 15:38). See further Hebrews 9:11–15, Hebrews 10:11–25.
15 “Therefore they are before the throne of God, and serve him day and night in his temple; and he who sits on the throne will shelter them with his presence.