Change is always subjective. All through evolution you find that the conquest of nature comes by change in the subject. Apply this to religion and morality, and you will find that the conquest of evil comes by the change in the subjective alone. That is how the Advaitic system gets its whole force, on the subjective side of man.
We can never lose what is really ours. Who can lose his being? Who can lose his very existence? If I am good, it is the existence first, and then that becomes colored with the quality of goodness. If I am evil, it is the existence first, and that becomes colored with the quality of badness. That existence is first, last, and always; it is never lost but ever present.