Green’s Dictionary of Slang

1. an overly religious person.

1838

Dickens Oliver Twist (1966) 159: He’s as willing as a Christian, strike me blind if he isn’t!

2. a tradesman who is willing to give credit, i.e. he ‘has faith’.

1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.