In Revelation 4:6 John has already introduced these living creatures to us. That passage had described God as seated on his throne, with the throne in turn positioned on “what appeared to be a sea of glass.” Around the throne of God (and therefore on the sea of glass serving as a floor) was an honour guard of “four living creatures.” From John’s description of these living creatures in Revelation 4:7, it is clear they were cherubim, that is, a class of angels. Since these living creatures served in proximity to God, they acted with more direct divine authority (think of a cabinet minister in a government compared to some other member of parliament). One of these four approached the seven angels exiting the sanctuary with these seven bowls. See also Revelation 6:1, Revelation 6:3, Revelation 6:5, Revelation 6:7.
7 And one of the four living creatures gave to the seven angels seven golden bowls full of the wrath of God who lives forever and ever,