Spirit is the great Player that gives rise to all those opposites equally — "I the Lord make the Light to fall on the good and the bad alike; I the Lord do all these things" — and the mystics the world over agree. Spirit is not the good half of the opposites, but the ground of all the opposites, and our "salvation," as it were, is not to find the good half of the dualism but to find the Source of both halves of the dualism, for that is what we are in truth. We are both sides in the great Game of Life, because we — you and I, in the deepest recesses of our very Self — have created both of these opposites in order to have a grand game of cosmic checkers.
That, anyway, is the "theoretical" answer that the mystics almost always give. "Nonduality" means, as the Upanishads put it, "to be freed of the pairs." That is, the great liberation consists in being freed of the pairs of opposites, freed of duality — and finding instead the nondual One Taste that gives rise to both. This is liberation because we cease the impossible, painful dream of spending our entire lives trying to find an up without a down, an inside without an outside, a good without an evil, a pleasure without its inevitable pain.
— Ken Wilber, One Taste