In that paragraph, the author, Charles Dickens, is describing different characteristics of the ancient religion of the Celtic inhabitants of pre-Roman England, the Britons. The detail ‘The Druid Priests had some kind of veneration for the Oak, and for the mistletoe’ illustrates how these people's beliefs were closely linked to their relationship with nature, in particular to trees and woods. In the next sentences, the author explains how woods were considered for them 'Sacred Groves', and how they used them like temples for their secret rituals and 'mysterious arts'. It can be inferred from the paragraph when Dickens says that today we hang up mistletoe in our houses during Christmas time, that some of these ancient practices may have survived in some features of our today's culture.