As with many of the scenes of Revelation, John is inspired to use an amalgam of more than one scene from the OT and even some mythical creatures from the Graeco-Roman pantheon (eg, Rev 13:1-5).
Rev 4 appears to be an amalgam of two scenes:
- The four cherubim of Eze 1 which had four faces, lion, ox, eagle, human, and attended the throne of God, complete with rainbow, and gleaming crystal around the throne
- The four seraphim of Isa 6 which have six wings and cry "Holy Holy Holy is the LORD of Hosts.
Note that the living creatures in Rev 4 are called neither seraphim nor cherubim.
The function of these two epiphany scenes in the OT have both similarities and differences.
- Both scenes are used to initiate someone to a sacred office - in both cases the prophets Isaiah and Ezekiel to the office of a prophet. Rev 4 & 5 appears to be the formal enthronement scene for the Messiah after His resurrection.
- Both scenes are placed in the heavenly sanctuary as is Rev 4 & 5.
- Isa 6 describes a worship scene as does Rev 4 & 5
- Eze 1 describes a functioning government scene where God is administering affairs in some sense, surrounded by obedient attendant. The same is seen in Rev 4 & 5.
Thus, Rev 4 & 5 imports the meaning of both Isa 6 and Eze 1.