What does Mark 1:23 mean?
Mark uses the Greek euthus (immediately) here again to mark an abrupt change. "Immediately" after Jesus reads the Jewish Scriptures and comments on what they mean, a demon-possessed man enters the synagogue. The ability to both teach well and control spirits is unique, leading to rapid popularity as well as jealousy among the religious elite.This is not the last time Jesus will have to deal with demonic possession. It's not clear why Jesus interacted with so many demons, or if demonic activity was just more common at that time. It's very possible that the demons had conflicting reactions to the Son of God—attracted to Him, angered by Him, and afraid of Him. Demon possession was blamed for many things in the New Testament that we would chalk up to physical ailments. For example, epilepsy (Matthew 17:15), or psychiatric disorders (Mark 5:3–5). It's very difficult, in modern times, to determine if someone is purely demon-possessed or suffering from a physical or mental illness. It would be dangerous to label everyone who is ill with demon possession, but we probably underestimate demonic involvement today.
The verse ends in the middle of a sentence with the phrase, "And he cried out." Unlike the crowd, the demon-possessed man interrupts Jesus' teaching. This is a direct confrontation between a man controlled by an evil spirit and Jesus. How Jesus deals with the spirit will reinforce His teaching and increase His fame (Mark 1:27–28).