I'm going to ignore the God part of believe, and simply say that what we believe informs our actions. What makes that an interesting viewpoint is that our actions can thus let others know whether we actually believe what we claim to -- or not.
So, for example, the Christian who enjoys telling people that "God is Love!" and who then goes one to say that "God hates gay people!" cannot be being honest. Each statement of belief totally contradicts the other. There's no way around that.
What about the person who thinks that "freedom" (as the Yangs in a Star Trek episode) is a "holy word?" If he then denies a gay man the right to marry the man he loves -- does he truly believe that freedom is a holy word? No, I don't think so.
This is the problem -- all humans believe some things so deeply that they couldn't possibly act in a way that defies their belief. I believe so strongly that a red, glowing burner on my stove will burn my hand horribly if I were to touch that nothing short of violence could get me to put my hand on it.
People who claim they truly believe in what Christ taught could not condemn others for being who they are. Those who zealously claim to love the Bible, and Matthew 25, who then deny help help to another person in distress -- I say that they do not actually believe what they think they believe.
40 “The King will reply, ‘Truly I tell you, whatever you did for one of the least of these brothers and sisters of mine, you did for me.’
41 “Then he will say to those on his left, ‘Depart from me, you who are cursed, into the eternal fire prepared for the devil and his angels. 42 For I was hungry and you gave me nothing to eat, I was thirsty and you gave me nothing to drink, 43 I was a stranger and you did not invite me in, I needed clothes and you did not clothe me, I was sick and in prison and you did not look after me.’
44 “They also will answer, ‘Lord, when did we see you hungry or thirsty or a stranger or needing clothes or sick or in prison, and did not help you?’
45 “He will reply, ‘Truly I tell you, whatever you did not do for one of the least of these, you did not do for me.’
In other words, they do not actually believe what they suppose themselves to believe. And when you don't believe what you think you believe -- then no, it doesn't matter at all what you believe. You'll be just as good or bad as you want to be, for your own reasons.
