'All flesh is not the same flesh: but there is one flesh of men, and another flesh of beasts, and another flesh of birds, and another of fishes. There are also celestial bodies, and bodies terrestrial. But the glory of the celestial is one, and the glory of the terrestrial is another. There is one glory of the sun, and another glory of the moon, and another glory of the stars, for one star differs from another star in glory.'
He points out that there are also many types of body. There are fleshly bodies. Men, beasts, birds and fish all have differing types of terrestrial body. But there are also heavenly bodies as well as terrestrial. And their glory is above that of the terrestrial, and each differs in glory. Thus there are the sun, moon and stars, and they all differ in glory. So may we also expect that the resurrection body will be different again, and again differ in glory.
We note that the earthly bodies are described in terms of flesh, although they do have a certain level of glory, while he speaks of the heavenly bodies solely in terms of glory. Thus the movement from earth to the heavens is a movement from a lower glory to a higher one, as all can see simply by examining the heavens. This is in preparation for speaking of the fleshly, terrestrial body of man, as connected with earth, becoming the glorious, heavenly body of resurrected man, as connected with Heaven, where all is glory, and yet as having a glory even greater than that of the heavenly bodies.
Paul was almost certainly thinking back to Daniel 12:2-3 where the resurrected dead were to shine as the stars for ever and ever. But he is careful not just to associate the new spiritual life with the glory of the stars, for they not only differ with each other in glory but are inferior to the resurrection body. At this stage he has on mind three types of body, fleshly, with its lower level of glory; heavenly and thus celestial and glorious; and spiritual, which we learn later has its own heavenly glory.
'There are also celestial bodies, and bodies terrestrial.' To catch his meaning here we may translate, 'As well as terrestrial bodies there are also heavenly bodies.' (Compare for a similar construction 1 Corinthians 16:18 a).