To me, what John's father is saying is that the law and the truth can change as time goes on. He is saying that things cannot stay the same forever.
To see this, look at the context of this quote. John has come back and has told his father the truth about what he has found in the "Place of the Gods." He tells his father to go ahead and kill him because he has broken the law.
But his father basically tells him that his actions have kind of changed the law. He has changed it by discovering a new truth and things will never be the same again.