Friend needs help with Plato's Republic

[Sonic]

here is his post to me. Any help or ideas are appreciated.
full text of the republic here: http://www.fordham.edu/halsall/ancient/p...public.txt

Colin L.:
I have hit a wall and really need some help. I am writing a paper on the Republic.
I need to describe how (619b-d) [the last 3 pages of the Republic mainly focusing on the myth of Er and rebirth cycle] sheds light on the overall argument of The Republic.
Describe how the following event sheds light on the overall argument of The Republic:

“the prophet said at the time: "Even for
the last comer, if he chooses wisely and will live diligently, there
is appointed a happy and not undesirable existence. Let not
him who chooses first be careless, and let not the last despair."
And when he had spoken, he who had the first choice came for-
ward and in a moment chose the greatest tyranny; his mind
having been darkened by folly and sensuality, he had not
thought out the whole matter before he chose, and did not at
first sight perceive that he was fated, among other evils, to de-
vour his own children. But when he had time to reflect, and
saw what was in the lot, he began to beat his breast and lament
over his choice, forgetting the proclamation of the prophet;
for, instead of throwing the blame of his misfortune on himself,
he accused chance and the gods, and everything rather than
himself. Now he was one of those who came from heaven, and
in a former life had dwelt in a well-ordered State, but his virtue
was a matter of habit only, and he had no philosophy. And
it was true of others who were similarly overtaken, that the
greater number of them came from heaven and therefore they
had never been schooled by trial, whereas the pilgrims WhO
came from earth, having themselves suffered and seen others
suffer, were not in a hurry to choose. And owing to this inex-
perience of theirs, and also because the lot was a chance, many
of the souls exchanged a good destiny for an evil or an evil for
a good. (619b-d)” -Republic

So, my problem is that I cannot prove/show that justice is good in and of itself because I view it as a means to another gain/reward. (Mainly coherence & protection between and from people, and as Plato describes in the Myth: the just soul will make the right decisions and as a result will be happy/healthy.)
One could say that Justice is good because it creates a healthy soul which in turn makes good choices. But that is in direct conflict with Plato’s stated goal: to show that justice is worthwhile even in the absence of the rewards it might confer.
I am in a loop here, and any help would be welcomed.
Thanks

[V-Man]

The justice that humans have between each other is nothing more than mimicking the natural concept of consequences.
Regardless of the attempts of people to build justice into their social systems, nature has its own justice that exists because it exists, not because someone proves that it is worthwhile or makes people happy.
However, it is important to note that good choices make the chooser happy, and very good choices make lots of other people happy (referring to the type of happiness Plato spoke of, not the type television wants you to believe in).
Because of this, people have had a tendency to enforce good choices on each other to ensure that communities and nations can have some progress toward happiness, branding this system "justice." When the justice system works properly, the community or nation actually does increase in happiness.

To address the concern about justice being "worthwhile" in the absence of its benefits, you should look at the inverse.
To fight against natural consequence (the self-existent justice) is more effort than accepting it and adjusting your life in accordance with it. How far would humanity have gotten if we had chosen to ignore the law of gravity? Rather, once we figured out the truths and consequences related to it, we have made entire systems designed to work with and around this law. In this specific example, Justice is served to those who ignore the law of gravity by removing from them the privilege of contributing to the gene pool.

So perhaps justice doesn't need to prove itself worthwhile, but it is very nice that it happens to bring happiness.

[Sonic]

damn. So much wisdom in so few words. Thank you so much.

[V-Man]

so few?
I was tempted to add tl;dr at the end. XD

[MykeGregory]

"i frag, therefore, i rule" -troll