The wheel within a wheel in its working indicates a globe.
The earth has to be redeemed first and this shall be known the Millennial reign of Jesus Christ . His kingdom on the earth merging with that of God is signified by the vision. He shall usher the new earth and the heavens. Nations of them which are saved …bring their glory and honor to it (Re.21:24) .nations of the earth are represented by the living creatures. The Number 4 always denote God’s agency for example as the 4 carpenters in the book of Zachariah(1:21-22).
Jesus Christ is the last Adam and he is indicated by the Man among the four creatures. ‘When he ascended up on high…and gave gifts unto men( Ep.4:8, Ps.68:18). The first Adam by disobedience brought curse and the last Adam brings a remnant of all nations to glory. (for further reading check out Guide to His Word-Ezekiel: Vision by the River Chebar)