To start with, Belief is a BIG word.
On a deeper analysis, we can understand that belief is something that is ‘perceived’ by us, ‘reasoned out’ by us in some sense.
Say, for example, you see something, you believe. A ‘direct’ physical perception. Sometimes, you perceive based on your mental or emotional learning and then believe – An indirect perception. “1 + 1 = 2” – A formula that says if you add ‘1’ to another ‘1’ it becomes ‘2’ – Fine, but why is ‘2’ called ‘2’ and why can’t 1 and 1 make ‘4’ ? – You have mentally perceived for a long, long time, that this is how it is and you believe whatever is based on it. If someone scolds you, then you are hurt – An emotional perception – ‘Hurt’ is hurt – You can’t define it in a physical form, still you believe there is something called ‘hurt’ as you emotionally perceive it.
There is another level of emotional perception. Say, you pray to your favourite form of God for a job, and in 15 days you get a job. Then, you start believing that form. Again, you need to perceive something physical(job) or emotional to believe that object of Power.
So belief is ‘perception’.
But, any belief’s life span is very unpredictable. It can turn around any moment. When Ptolemy averred that the Earth was at the center of the world, everyone believed it. Say, if you were to be transported to his period to convey the people that their belief was wrong, you would have been laughed at. But, if you were capable of touching at their mental or physical perception like how Copernicus(he said the Sun is at the centre) did, then your name would have been in history instead of his.
The basic meaning of perception, as given in www.dictionary.reference.com is ‘the act or faculty of apprehending by means of the senses or of the mind; cognition; understanding. ‘ Now, how could perception differ? – If you take a normal 5th grade child and ask him what ‘love’ is, she would say ‘Love is the kiss I get from my mother every day.’ The same question, I needn’t tell you, will surely fetch a different answer if you ask a college grad. So, it differs based on your so called maturity.
And, how much can one perceive? – If you take the same 5th grade child and teach her Integral Calculus, then will she understand? or at least try to imagine what it could be? A human mind can perceive 3 spatial dimensions, an ant can’t. Likewise, even the most intelligent human being on Earth has a ‘boundary on perception’, just like how an ant has. If an ant wants to perceive what a human can, then it has to become a human.
Thus far said about belief (perception), one biggest controversial topic based on belief, that has divided humans for eons, is that of ‘God’ [Next is Big-Bang Theory** :) ].
If God has to be brought under the scope of OUR belief, then She/He/It/??? doesn’t exist, because within our perception, there is nothing physical (with or without life), or mental, or emotional that is perceivable as ‘God’.
But there have been thousands and thousands of yogis or spiritual personalities on Earth, who have come to serve people, to console their sufferings, to clear their miseries, and who have asserted there is ‘God’!
Now, based on our existing emotional laws of human perception, won’t you believe someone who has done good to humanity without any expectation? Won’t you believe someone who has had no selfish motive to spread untruth? So, from that perspective, if a yogi has said there is God, then isn’t that to be believed?
Now, should I have to believe in God because someone whom I believe, perceives there is God, or should I have to disbelieve because I can’t perceive?
Ant Theorem solves issue: It says “If you can not believe ‘something’ because you can not perceive something, but at the same time you can not disbelieve ‘something’ because the one whom you believe perceives that ‘something’, then better understand that you are still an ant, and you should strive to grow to be a human to perceive that ‘something’.”
** If some one could explain that and things related to the theory in a simple and layman-understanding-manner, then there can be none better than Stephen Hawking in his wonderful book ‘A Brief History of Time’ – One of the most beautiful books I have come across.