From a religious viewpoint true magic would be power recieved from a supernatural being. Such as the ability to see the future like the girl that Paul cast a Demon out of.
The Jews were to avoid sorceries as things that would lead them away from God. But they were to embrace the miracles of God. Supernatural acts done by God.
What is the true differance?
The attempt to contact Demons would be wrong. But to act in a way to promote God with power recieved from God, is that wrong? The power recieved by the apostles was similar to the powers of the sorcerers, but on a much grander scale, a Holy Power as opposed to Black Magic.
When one uses the abilities given by God for God's good work you are doing right. But to seek out ways of gaining similar powers from sources other than God is wrong. Also to use powers given by God in a manner unpleasing to God is wrong. In this way "magic" can be similar to "speech." But not everyone wants to be a good speaker, but many unfortunatly want to have a magical ability.
As an addendum, what about the difference between Gandalf and Sauron? Is Gandalf evil, even though he has the same abilities as the obviously evil Sauron?