Christian Bale plays the starring role as Moses in the forthcoming movie epic Exodus: God and Kings but from recent comments, it sounds like he had to do some homework for the role.

In a Q&A following a screening at 20th Century Fox, Bale described the character of Moses - and God, for that matter - as "mercurial", according to The Hollywood Reporter.

"The big one for me, other than realising I had no idea about Moses at all, was just how complex a character he was," he said.

"He was a very troubled, tumultuous man and mercurial.  But the biggest surprise was the nature of God.  He was equally very mercurial."

He admitted during the Q&A that his Bible knowledge was rudimentary, in his own words "below Sunday school".

To fill in the considerable gaps, his reading preparation included the Torah, Jonathan Kirsch's Moses: A Life, and the Koran, The Hollywood Reporter says.

He also sat down to watch the 1956 classic The Ten Commandments, starring Charlton Heston, and for a bit of light-hearted inspiration, Monty Python's Life of Brian.

Exodus: God and Kings is directed by Ridley Scott and is due to hit theaters on December 12.  Starring alongside Bale is Joel Edgerton as Pharaoh Rhamses and Sir Ben Kingsley as Nun, the father of Joshua.

Sir Ben, who played the title role in the film Ghandi, said he tried with his work to "demystify" figures of note "and say, Look, these guys were fresh for blood, and they had a hell of a struggle".

He said Bale's performance as Moses was "beautiful".

"But you see it's gritty," he continued.  "It's a guy struggling, and sometimes very out of his depth."

The film follows Darren Aronofsky's Noah, which starred Russell Crowe and grossed $359 million at the global box office.

Other faith-related releases to the big screen this year include Heaven is For Real and God is Not Dead, both of which performed well at the box office.