Oxymoron would be the correct answer
This quote means to describe the root of the deprecation of many people to properly conduct an investigation about any subject, and that root is lack of interest. In order to do something right, one must concentrate on that subject alone, ignoring all other distractions, but that can only be achieved if the investigator feels drawn to the subject - meaning they find it interesting.
Lack of interest is what accomplishes to "keep a man in everlasting ignorance...". In the case of ignorance, the investigation might go through, but it will most likely consist of a mindlessly structured compilation of other people's research which the investigator would hardly be able to interpret.
