Pure monism and pure dualism do not understand and therefore reject the mystery of freedom; they regard evil from an exterior point of view without grasping its inward origin.
Either evil finally disappears or it appears as a force completely outside and apart from the human spirit. But if evil cannot be regarded as having its source in God, and if outside God there is no other source of being, how can the phenomenon of evil be explained.
How can this dilemma be resolved?
To the Christian way of thinking neither monism nor dualism is right, and it has its own peculiar solution of the problem of the origin of evil. For Christianity this question is connected with that of freedom and cannot be solved apart from it.
Indeed monism and dualism both involve the denial of freedom, and are thereby incapable of comprehending the phenomenon of evil. The interpretation of the mystery of evil through that of freedom is a suprarational interpretation and presents reason with an antinomy.
The source of evil is not in God, nor in a being existing positively side by side with him, but in the unfathomable irrationality of freedom, in pure possibility, in the forces concealed within that dark void which precedes all positive determination of being.
Thus evil has no basis in anything; it is determined by no possible being and has no ontological origin. The possibility of evil is latent in that mysterious principle of being in which every sort of possibility lies concealed.
The void is not evil, it is the source of every kind of life and every actualization of being. It conceals within itself the possibility of both evil and of good. An initial, irrational, and mysterious void lies at the heart of the whole life of the universe, but it is a mystery beyond the reach of logic.