Daemonologie is short, and it is written in the form of a dialogue between Philomathes, who has doubts, and Epistemon, who removes them. The doubts are not invented for the occasion. They are the arguments of Johann Weyer and Reginald Scot, and James VI names both in his preface, which is the clearest possible statement of what the book is for.
The three books cover magic and necromancy, then sorcery and witchcraft, then spirits and possession. The position is firm throughout: the pact is real, the crime is real, the Devil's power is genuine though permitted by God, and the magistrate who fails to prosecute fails in a duty. The reasoning is conventional demonology, competently marshalled. What is unusual is the author. Sixteenth century Europe had many demonologies and no other written by a reigning monarch, and the difference shows most in the tone: this is not a scholar persuading readers but a ruler settling a question that had been raised in his own kingdom.
It had been raised there in the most direct way. In 1590 and 1591 James was personally involved in the North Berwick trials in Scotland, in which a group of accused people were said to have raised storms against his ship. A king who has sat through confessions describing an attempt on his own life has a stake in their being true, and readers of Daemonologie have noted that connection since it was published.