Simply put, justice is a human creation, a tool, used to bring harmony to an otherwise chaotic state of being. I say "human creation", as I see no indication that justice is commanded by some divine presence or even something which merely exists in the universe as a force of nature. And I use "tool" loosely, as we are naturally inclined to preserve our community and will punish those who violate the laws and norms of our society. As Cicero noted, we are compelled to do good and defend our community. From this inclination, justice arises.

However, I must add that there is a distinct difference between justice and vengeance. Justice is impartial and fair. Through justice, the society as a whole is benefited. It is selfless.

Vengeance is biased and personal. It only succeeds in perpetuating harm and bringing a hollow and fleeting sense of satisfaction to the one seeking vengeance. It is a wholly selfish endeavour.

Justice does exist as a human creation. It is flawed, because humans are flawed.