Backslider n. : One who backslides.

Example:
Why do christians hate the Backslider more then a non- christin?

Taxonomy
backslider, Wiktionary, Etymology, Pronunciation, free dictionary, search, Rudyard Kipling, The Judgement, Black and White, Folio Society, vol. 1, Red Elephant, Elephant Tusk, hills, faithful, God, Things as They Are, the backsliders.

Defination from the web:
... the hills, and the faithful waked and said: The God of Things as They Are matures revenge against the backsliders. ... She married him thinking to change his ways, and for a while he got religion, but he was ever a backslider; she soon began finding bottles stashed about the house. ...