Answer :
Unlawful based upon the context given mostly means sinful, forbidden and unnatural. Dr Faustus who is not satisfied of what he had studied (medicine, logic, law and theology) sold his soul to the devil in exchange of great power for twenty four years using magic.
The answer to your question which is Based upon the context, the word unlawful most likely means -sinful and-forbidden. In this passage, those things that are considered as unlawful are those things that are not right and sinful. Those things are also forbidden because of its consequences.