One way of understanding this is in terms of polarity. This is the idea that dark and light, male and female, up and down, good and evil, and any number of categories are not opposites, but polar like the north and south pole. One implies the other. If you try to cut off the south pole, there is another one underneath. Also, if you have a north pole, you can be certain that there is a south pole.
So in this way, inner implies outer, upper implies lower, and male implies female. It seems to be our condition, however, to think in categories of this and that. We want to DEFEAT evil, or see in 1 John that God is light and there is no darkness in him. Or in Revelation 22 that there will be no night in the kingdom to come.
But this is like trying to have a mountain range made up entirely of peaks and no valleys. You might also compare this to "The way of the lord" in Isaiah 40 (a core reference in all canonical Gospels). There:
Isaiah 40:4, "Every valley shall be lifted up, and every mountain and hill be made low the uneven ground shall become level, and the rough places a plain."
Here, this author clearly understands the idea of polarity and the revelation of God when the separation of the poles are eliminated. You can also see this in the reunion of male and female as one flesh (Genesis 2:24).
You can also see this in the way that the Jews meet at dawn and dusk to make offerings to the Lord (Numbers 28). While they also provide a sabbath (sun/light) and monthly (new moon, darkness) offering, the offerings to the LORD take place at dawn and dusk when God is present in the intersection.
There are many places where the intersection of these polarities is seen behind a Christology in the text. Jesus is also human and God which are polar opposites. Jesus is the immanent and is in relation with the transcendent, and it is this intersection of that polar pair that God is present.
So for this particular line of theology, God is the continuous intersection of polar principles. Light and dark are continually and eternally crashing together and being separated at dawn and dusk. Male and female are continuously coming together, not just in sex, but in a sort of giving and receiving.
So in this way, you can read Thomas as speaking to this truth. The kingdom will be revealed when you realize the unity of the poles (as Thomas declares "My Lord and My God" in John 20), but this realization is a mental shift, and not a physical shift. The world is ALREADY like this, it is just that you now see it. So in this case, nothing really changes. The things of the world are still themselves. A foot is a foot... An eye is an eye... and image is an image.
This goes with Thomas 113
His disciples said to him, "When will the kingdom come?"
"It will not come by watching for it. It will not be said, 'Look, here!' or 'Look, there!' Rather, the Father's kingdom is spread out upon the earth, and people don't see it."
This is present in the canon in Luke 17:20-21. Here, Jesus is not saying that the "kingdom come" is something that will happen physically, but that it is a psychological transformation.
This is captured in how Jesus "defeats satan" by submitting to the cross. He doesn't put his fists up to fight evil, but puts his hands out. It's somewhat counter-intuitive, but it's very much like the chinese finger trap. Polarity is a theology of non-dualism and there is strong support for it throughout the canonical scriptures.
I believe what the first century authors were struggling with was a semantic shift created by their time as a Vassal state to Zoroastrian Persia between liberation from babylon by Cyrus (Isaiah 45:1), and the conquest of Alexander into the Helenistic period. While the Jews once had this theology of polarity, the polytheistic influence of the Zoroastrians began to demonize the dark and shift towards light (in Zoroastrianism Light = Good, Dark = Evil). It seems that some first century authors saw Jesus as a return to orthodoxy of polarity and monotheism instead of what seems like a polytheism of a purely Good God with no evil at all.
In this way, Jesus is the birth of the darkness back into the world in order to divinize it (being born liturgically at the winter solstice), and he is revealed as God at the vernal equinox (Easter) when light and dark are perfectly balanced, just as in Numbers 28.
Thomas is Good stuff. I'm Glad you asked this question. I hope that this helps.