What does the Bible say about evil spirits?

In Acts 19, the scripture reveals that evil spirits have knowledge of Christ and His authority. One instance shows an evil spirit acknowledging Jesus and being acquainted with Paul, stating, 'Jesus I know, and Paul I know, but who are you?' (Acts 19:15). This indicates that evil spirits recognize the divine authority and power of Christ over them, which they acknowledge with fear. The passage emphasizes the importance of understanding both the reality of evil spirits and the sovereign power of Christ to overcome them.