Hello Tomas,
I believe that the jest of it is that in the Allegory of the Metals we see a division of class, I believe these classes are the ruler-who is gold, the guardian-which is silver, and the craftsman- which is lead or bronze. In a sense it is not really a division of class as one might see in most societies based on wealth, but rather a balance. The Craftsman are the producers and sellers of services, the guardians are the soldiers, protectors, etc. and the rulers are just that. A person is said to be born with a certain characteristic for one job the other, and this is the job that he is meant to pursue and thus there is harmony. Another point to state is that the guardian can become a ruler, but otherwise no class crosses into another.
The point that I think relates most predominantly on the Allegory of the Cave is the idea of the ruler as a philosopher-king. The philosopher-king is the only one of the society that travels beyond the cave. He may teach the others in society about the illusions of the cave, etc. but often times they do not believe what he says as illustrated in the passage.
This is just a basis on the query. I found a very good source which you might want to take a look at. It discusses these ideas further and I think you will find it helpful.
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http://www.toptown.com/nowhere/mvdorf/essay/plato.html>;
Good luck with your work. Thank you for visiting.
-Platonia.