Spee wrote as a Jesuit priest addressing magistrates, advisers, confessors and others involved in the trials. His argument did not require denial of the supernatural. It required a distinction between believing that evil exists and proving that a particular accused person committed an alleged act.
Torture was central to the problem. A confession obtained through pain could reproduce the interrogator’s expectations rather than the truth. Names supplied under such conditions could lead to further arrests and apparently corroborating statements generated by the same mechanism. A growing file could therefore contain more repetitions without containing more independent evidence.
The work also examined the pressures surrounding a defence. An advocate or confessor could fear suspicion for questioning the charge. Spee insisted that the seriousness of the accusation strengthened the need for reliable procedure. Official position and sincere zeal did not remove personal moral responsibility for the consequences of a defective process.
The book did not immediately end witch trials, and its influence should not be exaggerated into a single-cause explanation. It remains an important witness to Catholic criticism from within early modern Christian society. Together with Salazar’s investigation and the Spanish instructions of 1614, it demonstrates that rigorous evidentiary restraint could arise from religious conscience and institutional review, rather than only from an external rejection of Christianity and its account of moral responsibility.