Give meaning to such meaningless, human created pain. This construction justifies man's evil for the Christian and the pagan, for the lawgiver and the law breaker, the creditor and the debtor, the master and the slave, the father and the child. Thus philosophers, in turn, created free-will to keep the gods interested in the human play. A determined world would provide no interesting spectacle. Existence can't have meaning without pain having meaning.
External meaning is festive- action.
Internal meaning is guilt- reaction. I'd wager, rather, chance. Nietzsche does ascribe some meaning to pain. Pain is not an argument against existence. Today people avoid pain.