How does a witch have power? I will explain it with criticism, and a word of warning to anyone who practices this evil.
A witch doesn't have power, nor does a christian. When a witch makes a ritual or creates what is called a magic spell, it is a prayer or command to a demon. That demon goes about to cause the evil the witch has asked or demanded. This is true for a christian. Except the christian asks their God, Jesus Christ, they pray to God. God will make it happen, or send angels to make it manifest. Even sending other Christians. In witchcraft, the demons will also gather evil people to perform the evil deed.
This is why it is a problem for the witch. The demon's tactic is to steal, kill and destroy. The demon's desire is to kill, steal, and destroy the witch that is commanding it. This is where blood sacrifices and chants come from. The demon requires that the witch sin against God. This causes the witch to make God angry with them. That means the witch is on the path to hell, now the demon will give the witch their desire.
The demons are always trying to kill the sinful witch because they will be destroyed in hell if they perish. The demon also will try to kill the individual the demon was sent against. The devil's desire is for all man kind to suffer for eternity. The devil and Satan are pure evil, they have no good in them.