The type of mind that can understand good fiction is not necessarily the educated mind, but it is at all times the kind of mind that is willing to have its sense of mystery deepened by contact with reality, and its sense of reality deepened by contact with mystery.
We lost our innocence in the Fall, and our turn to it is through the Redemption which was brought about by Christ's death and by our slow participation in it. Sentimentality is a skipping of this process in its concrete reality and an early arrival at a mock state of innocence, which strongly suggests its opposite.