A person's actions have nothing to do with their belief in God.
Of course it is, if you don't follow Gods word every moment of everyday why should anyone believe it when you say you believe in him.
I can say I believe in God but if I act like a twat its a meaningless statement.
If you truly believed in God and his message and the consequences for not following the word of God then you would never do anything contrary to his word.
Jordan explains it much better