Spiritual excitement takes pathological forms whenever other interests are too few and the intellect too narrow.
 William James, The Varieties of Religious Experience (1902). copy citation

Context

“In the life of saints, technically so called, the spiritual faculties are strong, but what gives the impression of extravagance proves usually on examination to be a relative deficiency of intellect. Spiritual excitement takes pathological forms whenever other interests are too few and the intellect too narrow. We find this exemplified by all the saintly attributes in turn—devout love of God, purity, charity, asceticism, all may lead astray. I will run over these virtues in succession. First of all let us take Devoutness.” source