The authors seem not to understand the topic unfortunately and have to use long prose as they are trying to wrap their head around it.
The core problem and idea for solution is actually quite simple. Let me condense the topic into a tweet or two.
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Problem: You have a naturally occuring resource which is scarce and which nobody created. How do you allocate it to humans?
Solution: Georgist simply say you can use an auction granting you possession for some amount of time instead of giving you time unlimited rights just because you were first to ask to use it.
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This is not a theory as it is applied in many systems such as DNS allocation or electromagnetic spectrum allocation. Georgists point out that similar allocation problem is for "land" (think location) and the same auction mechanism can be applied.
Land was considered abundant in the past, especially as new continents were being discovered. Therefore nobody though about allocation, same as nobody considers allocation of air. If air got severely polluted (say by radioactivity) and only small fraction remained usable for humanity, you can be assured that the same allocation problem would exist for air.
After discovering all continents on Earth land ceased to be abundant and now requires a proper allocation mechanism. Otherwise landlord monopolies will continue piling up profits because of their luck in winning the infinitely durable possession rights allocated years, decades and centuries ago in badly structured auction.
Either we start inhabiting new planets or we solve problem of allocation of important scarce resources.
What's funny - you solve this allocation problem and many societal problems disappear as if by magic. Somehow this suggests that land allocation is a major root cause of society.
That's why Georgists dwell on it so much. You should start solving problems from the most serious ones with high impact.