
The iconography here plainly signifies, not the material composition of the finite universe, but the Orders of Creation and Redemption. You have Jesus Christ, Pantocrater, Who Rules over the entire fabric of created reality, Heaven inclusive. Here we see the Church Triumphant, Militant, and Suffering; and also the chasms of hell.
The phraseology of the Church typically makes the earth the relative center of all things, by designating locations in relation to it. Thus Heaven is above the earth, and the realms of Purgatory and Hell are under the earth. This icon perfectly represents such phraseology. The globe in the middle represents the earth, God's footstool.
What is interesting philosophically is the idea of motion. There is no absolute motion in hell - you are fixed there for all eternity. The same for Heaven, Eternal Beatitude in the Eternal Present of God. Interestingly, Purgatory, which is closest to earth, is characterized by some motility. Purgatory is not a fixed abode, thus there is real motion there. Note that there are Angels in Purgatory helping to raise souls up, and that the highest souls in Purgatory are beckoning the earth, from whence they receive indulgences. The bodies in hell are facing downwards, where they will fall, in merely apparent motion, for all eternity.
My takeaway from this icon is twofold: One, that there are both logical and theological reasons why the earth must be fixed in the center of the universe. And perhaps this is why the Church explicitly teaches geocentrism.
When we think of the centrality of the earth, and especially because we think in therms of a sphere, we envision concentric rings with the earth in the center. A lateral, 2-dimension plane of sorts. But if we think directionally, which is much more in keeping with the phraseology of the Church, we locate things in accordance with their position relative to the earth - above or below.
The very word 'footstool' signifies the idea of beneath.
Secondly, Christ, Who is not only our Creator, Redeemer, and King, but also our Teacher and Exemplar, is certainly going to rest His feet on the earth, the location of the greatest flux, change, and movement, the place of the greatest danger to souls, and of the greatest need for His constant intervention.
Rule Thou in the midst of Thy enemies.
How beautiful are the feet of them that preach the gospel of peace, of them that bring glad tidings of good things!Upon the earth He rests His feet,
Upon the earth where there is no rest.
The foxes have holes, and the birds of the air nests,
But the Son of man hath not where to lay His head.
For upon the earth, there is no rest.