You can use science to answer the question, "Why is blood red?", but you cannot answer the question philosphically (to do so would require that you explain why the laws of physics exist in as the convention which we know them to be). "Why is blood red?" is a part of deeper questions.
For those who believe in God, the question is, "Why did He choose to make the universe, and life as He had chosen to create it, the way that it is? (If you do not believe in God, blood will still be 'Red'). This asks a still deeper question: We understand red to be 'red' because we had been taught that the color which we see, as red, had been named 'Red'. It could have been named 'Zap''. It had been named 'Zap', the question would have been posed, "Why is blood, zap?" The same convention that red is named "Red" is obvious if you speak a language in which red goes by another name.
This holds true for our word for God. Likewise, so too, "THE BIBLE". And too, the words in The Bible. Also, truth. The matter becomes a personal interpretation of everything in reality, including that there is such a thing as reality, and that reality remains consistant over time. Existentialist angst aside, reality is NOT consistant over time. As you grow up, from infancy, your understanding of realty changes, (assuming that you develop in to adulthood).
Therefor, the question, "Why is blood red?" can not be answered as an absolute. For that matter, our understand of what is and is not religion, and our understanding of God cannot be assured. (As an absolute).
Strange creatures, we.
Assuming that you believe in God (or Gods, as the case may be), and that God in your faith has a similar convention to our generic concept of God per se. We, each in our own faiths, need a convention of God and of many other things in life, or else we could not function either as a being or as a member of the (your) faith. Usually, we assume reality to be a universal set of conventions, and seldom attempt to function outside of these common conventions, so that we can function. Technically, our conventions of what we perceive reality are what to be have assumed. Functioning outside of these sets of conventions, except for philosophy or for inquiry, is insanity.
Both differences between faiths, denominations, sects, or other divisions within your faith, that which we differ from one another (for seeking an absolute truth, "THE TRUTH"), can be both the cause of mutual freindship, or hatred, division, war, death, dysfunction, and destruction (insanity). Do we need the very faiths that we hold to be 'universal' which can unite us or divide us to answer these questions, establish a set of conventions which we accept to be God, and everything else in faith? People who either do NOT believe in God, or are uncertain as to which path to take to find the truth may argue, perhaps, that this supports their belief that there is no God. It cannot prove that to others, it can convince them of their own beliefs.
