Jesus was a great preacher and teacher and his miracles were something the world had never seen before. He was also a great debater, so neither the Pharisees nor Scribes were able to stump him with any of their questions. His popularity was increasing and so he became a threat to the Jewish establishment of his time.
In the Gospel reading, taken from Mark 3: 20-30, Jesus was accused of casting out demons by the power of Satan—Beelzebub. This was an absurd suggestion because this implies that Satan was casting out Satan. In reply, Jesus said, “How can Satan cast out Satan. A kingdom divided against itself cannot stand.” (Mark 3: 23) The Pharisees were resorting to this type of accusation because they had tried everything else and nothing worked. Calling Jesus Satan was a tactic of desperation.