Jesus said that within the kingdom of God there exist "wheat and tares" and "sheep and goats." There are genuine and counterfeit Christians, as well as genuine and counterfeit doctrine and genuine and counterfeit signs and wonders. Since the possibility of being deceived is real, we must exercise discernment lest we be led astray. When genuine signs and wonders occur, no one is left in any doubt that a supernatural event has taken place. Even those who denied God acknowledged his miracles.
Pharaoh's Magicians
The first three plagues of the ten God sent upon the Egyptians were 'duplicated' by Pharaoh's magicians: "Pharaoh then summoned wise men and sorcerers, and the Egyptian magicians also did the same things by their secret arts." (Exodus 7:11, 22, 8:7) Had the magicians not been able to give a convincing demonstration of power they would not have been kept in Pharaoh's employment. But their 'secret arts' quickly reached their limitations. When the fourth plague came "the magicians tried to produce gnats by their secret arts, they could not... The magicians said to Pharaoh, 'This is the finger of God.'" (Exodus 8:18-19) The magicians did amazing things, and people believed them, but their power did not come from God.
Simon the Sorcerer
Philip the evangelist encountered a sorcerer when he preached the gospel in Samaria. "Now for some time a man named Simon had practised sorcery in the city and amazed all the people of Samaria. He boasted that he was someone great, and all the people, both high and low, gave him their attention and exclaimed, 'This man is the divine power known as the Great Power.' They followed him because he had amazed them for a long time with his magic." (Acts 8:9-11) Simon would not have had a great following if what he did was not spectacular and defied explanation. He must have been convincing because he was believed by "all the people, both high and low."
Yet what Simon did and what Philip did were as different as night and day. "When the crowd heard Philip and saw the miraculous sings he did, they all paid close attention to what he said. With shrieks, evil spirits came out of many, and many paralytics and cripples were healed. So there was great joy in that city." Even Simon was "astonished by the great signs and miracles he saw." (Acts 8: 6-8,13) The genuine miracles performed by Philip exposed Simon as a fake.
When the power of God was displayed those who engaged in false signs and wonders, such as Pharaoh's magicians and Simon the sorcerer, acknowledged their limitations. Their special powers could not stand up to the power of God.
The Effect of Jesus' Miracles
Jesus' miracles astonished those who saw them. We'll take just one example. A paralytic man was brought by his friends to Jesus. Unable to get into the house where Jesus was, they proceeded to lower him through the roof into the presence of the Lord. Jesus said to the crippled man, "I tell you, get up, take your mat and go home." The Bible tells us what happened next: "He got up, took his mat and walked out in full view of them all. This amazed everyone and they praised God, saying, 'We have never seen anything like this!'" (Mark 2:11-12)
Though sorcerers and exorcists were active in that society, when Jesus healed the crippled man the people unanimously declared, "We have never seen anything like this!" And that will always be the response when people witness the divine power of God.