Cave symbolizes the conditioning of your mind, the training you had gone through, your experiences: defeats and victories, your philosophy of life

Light symbolizes the realities that govern the world. But because of many schemes and devices of man, It cast shadows of the realities of life in a pretentious way that the common man was blinded to see the truth. Though they might have seen the truth, it paralyzed them to break off from its system-chain.

This allegory explains to me that you should not come to conclusion and judge others without knowing the truth.
Don't be fooled by the shadows of realities.
And the first-hand experience makes you understand better the world you are living in.
If you were able to come out of the cave and have seen the light of truth, help others to come out of their caves and they might behold the real things.