Celsus talked quite a bit about Christians in his writings (he wrote On The True Doctrine as a response to Christian teachings). As Christianity was starting to make small ripples during his era mostly because of their counter cultural views, he wrote arguments against the early church by focusing on three things: 1) Refuting its philosophical claims 2) Claiming it was a phenomenon associated with the uneducated and lower class and 3) by claiming it was a threat to Rome.
The reason I began with the quote has to do with the fact he honed in on something Christians did that was counter cultural that we—in the modern age—view as something that would have been barbaric (slaves and treating women as inferior). The point being that we must return to our roots as stated in the article. Hope that explains it a little more!