what's the meaning of this sentence?

No, the Bishop of Cashel was an officer of the "Church of Ireland," which was really just an extension of the Church of England into Ireland. It appears that the Bishop of Cashel sold off some of either his personal property, or some property of the Church of Ireland.

It appears that there is a typographical error in your text. There is such a thing as the Mazarin Bible (no "e" at the end of the first word). It is another name for the 42 line bible printed by Johannes Gutenberg sometime in the 1450s. Only about 20 copies or so still survive. It was the first book printed in the West with moveable type, and it started a communications revolution which profoundly changed the world. It is considered the most valuable printed book in the world.

When Mr. Quaritch purchased a copy for 595 pounds (referring to pounds sterling, the English currency), he got a bargain. Apparently, he later paid 4000 pounds for another copy of Gutenbertg's 42 line bible, the Mazarin Bible. The last time a copy of this book was sold, sometime in the late 1970s, it sold for more than $2 million dollars US. It should be easy enough to get the details of that.