The philosophy of religion is a branch of philosophy dealing with questions of a religious nature: What is God? Does God exist? If so/not, what does this mean for us? It deals with the nature of religious experience, miracles, good and evil, morality, the relationship between science and religion, the afterlife and much more. It is by no means exclusive to the sense of God of the Abrahamic religions, and also deals with polytheistic, pantheistic, and atheistic views. In this sense the word "God" is more of a catch-all used to frame a particular set of beliefs about the world.
What is God?
The question "What is God?" must be answered in order for meaningful discussion to take place. Because there are so many different senses of the word "God" we must be clear about which conception we are dealing with. The Abrahamic religions believe in a single, supernatural God (monotheism). Hindus are somewhere between monotheism and polytheism, believing in many different deities which are all manifestations of a single God. Mahayana Buddhism and Tibetan Buddhism are two polytheistic belief systems, while Theravada Buddhism is atheistic in nature. These are but a few of the belief systems addressing the nature of God, and this diversity accounts for much of the breadth of the philosophy of religion, and is why we must answer "What is God?" before other questions, even "Does God exist?"
Does God exist?
The second important question to address is whether we have good reason to think that God does or does not exist. There are three main positions one may take in response to this question:
I. Theism: the belief in the existence of at least one deity or divine being
1. Pantheism: God exists as all aspects of the universe. God is all, and all is God, and there is nothing else. Taoism & Hinduism are generally considered to be pantheistic. (Taoists don't conceive of any God in the Western sense)
2. Panentheism: God encompasses all aspects of the universe but is also greater than the universe. Abrahamic religions often take this view, though not universally.
3. Deism: God exists but does not take part in the universe after having set it in motion.
II Agnosticism: the belief that the existence of a God or gods is both unknown and unknowable. Agnostics may choose to believe that God exists or doesn't exist, agnostic theism and agnostic atheism respectively, despite the belief that we can never know for sure.
III Atheism: the absence of any belief in deities.
Attempts to prove the truth value of the proposition "does God exist?" will depend upon the individual's stance as outlined above. There are three such classical arguments (of Western origin):
ontological argument: Attempts to prove the existence of God using reason alone, without the need for empirical evidence.
cosmological argument: Is based on the law of cause and effect, stating that the origin of the universe must have been caused by God.
teleological argument: Is based on the perception of order, purpose, design, and in nature - the fact that the universe seems "fine tuned" for human life.
What does it mean for us?
Answering the questions "what is God?" and "does God exist?" allows us to consider a huge number of other questions with implications for our lives. Such questions include:
Do we have freewill?
Why is there evil?
Do our lives have purpose? If so what is it?
Do morals exist? If so what are they?
Do miracles happen?
What is the nature of consciousness or human experience?
The philosophy of religion is important because most people ask themselves these questions at some point in their lives. The answers they find shape the way they structure and lead their lives.