Similar to The Hitler Card, The God card is when one evokes the name of God or some other religious deity into a debate. Usually their logic is that their opponent's position goes against the word of God and often times they include religious scripture. This is Usually done as alast ditch effort by someone who does not have anything even remotely resembling rational reasons for their position and feels the need to appeal to their opponents religious beliefs or blind faith to steer the argument into their religon.
The God Card often comes into play on issues like abortion, war, or politics.