As Socrates transitions from the proper praise for both men and gods, he then also introduces some guidance for how poetic depictions in his ideal city are to represent the afterlife, with particular consideration for how this will affect the guardian class. 

“And what if the men are to be courageous? So then should not one say such things so to make them fear death least of all?  Or do you think that someone with this fear in him would ever become courageous?”

“By Zeus,” he said, “I do not.”

“What, then?  Do you think anyone who believes in Hades and that it is terrible would be without fear and during battle would choose death before defeat and slavery?”

“Not at all.”
(Republic, 386a6-b7).

The problem Socrates identifies is that we understandably want to have courageous guardians.  Yet the tales traditionally told of Hades (the afterlife), at least some of them, tell us that the dead are gibbering, incorporeal wisps of humanity, mere shades who, even at their best, are worse than the worst estate of any living human.  If this is the case, there are few, if any, guardians who, although preserving the city by their own death, would willingly sacrifice themselves for a dismal and horrid afterlife.  Socrates’ solution is to ban poetry which relates this type of undesirable afterlife from his republic. 

On the other hand, if the poets only rhapsodized about the delights of the paradise yet to come, the guardians would not only be willing to die for their city, but they would positively jump at the opportunity to die in battle and consequently enter into heavenly bliss. 

There are some intriguing considerations that this scenario raises. It is obviously jarring that Socrates is not interested here in whether the tales these poets are raising are true, in either a literal or metaphorical sense.  It may be the case that there really is a hell, to use our term, and that some actually go there.(2)  But Socrates’ concern is more calculatingly practical, fixating on the overarching political need to have soldiers whose courage will not be blunted by a fearful avoidance of death.   

Furthermore there appears to be a tension between the incentives of good citizens and those good guardian-soldiers.  It seemed that in the first book of the Republic the worries of being unjust and base prompt one to behave in a just way, lest one die, be judged and depart into the hopeless abyss of Hades.  In the case of the guardians, however, the edifying influence of the fear of Hades is banished, at least by poets and poetry. 

REFERENCES:

(1)
Τί δὲ δὴ εἰ μέλλουσιν εἶναι ἀνδρεῖοι; ἆρα οὐ ταῦτά τε
λεκτέον καὶ οἷα αὐτοὺς ποιῆσαι ἥκιστα τὸν θάνατον δεδιέναι;
(b.) ἢ ἡγῇ τινά ποτ’ ἂν γενέσθαι ἀνδρεῖον ἔχοντα ἐν αὑτῷ τοῦτο
τὸ δεῖμα;
Μὰ Δία, ἦ δ’ ὅς, οὐκ ἔγωγε.
Τί δέ; τἀν Ἅιδου ἡγούμενον εἶναί τε καὶ δεινὰ εἶναι οἴει
τινὰ θανάτου ἀδεῆ ἔσεσθαι καὶ ἐν ταῖς μάχαις αἱρήσεσθαι
πρὸ ἥττης τε καὶ δουλείας θάνατον;
Οὐδαμῶς.

(2)
Contrast this with the myth of Er at the end of the Republic, which indeed does posit a hellish afterlife for the wicked.