Notice the anthropomorphic language—all the descriptions of human traits and behaviors—of this passage. In verse 3, for instance, the Two Witnesses are clothed in sackcloth. How could this apply to two parts of a book? Most of our Bibles are "clothed," if you will, in leather bindings or cardboard and cloth covers. It takes quite a bit of mental gymnastics to see how one can fit this type of terminology into the idea of the Two Witnesses being the two books of the Old and New Testaments. A person must symbolize away nearly the entire description of them.
Also notice verse 6: "They have power . . . to strike the earth with any plague as often as they wish" (The New Testament in Modern English by J.B. Phillips). In other words, these Two Witnesses have the power of volition, or will. They can make decisions, and they can execute them within the scope of the power God has given them. The Old and New Testaments are not animate beings with minds of their own, and as such, those two collections of books cannot express volition. They cannot make decisions, nor can they execute decisions in this sense.
In verse 7, the Two Witnesses die, and they are described as having bodies that lie in the streets of Jerusalem. Admittedly, we can refer symbolically to the death of an idea. We can describe the end of an era as a kind of death and so forth. However, death in this passage does not appear to be metaphoric because God speaks of their bodies lying in the street and remaining unburied. This type of language is not amenable at all to understanding the Two Witnesses as the Old and New Testaments.
Then notice verse 11: "The breath of life from God came into them" (The New Testament by Richmond Lattimore). Are there any known instances of God breathing life into books? The idea of them being the Old and New Testament becomes even more ridiculous when we realize that the Two Witnesses then stand on their feet—this is a real resurrection—and they are translated to heaven!
In verse 10, John actually uses the word "prophets." In Greeks, it is the word prophetes (Strong's 4396), which appears about eighty times in Scripture. This word is always rendered in the King James Version as "prophet" or "prophets." For instance, Jesus uses the word in Matthew 13:57: "A prophet is not without honor except in his own country." There is not one instance where this Greek word refers to the Scriptures; it always refers to a person or to people.
A great deal of other evidence exists as well. For example, Revelation 11:3 tells us that God empowers His Two Witnesses for a limited period of time, 1,260 days. But does God ever set a time limit on the power of His Scriptures? God does not, in fact, set a time limit on the power that He gives His Word. Notice Isaiah 55:10-11:
For as the rain comes down, and the snow from heaven, and do not return there, but water the earth, and make it bring forth and bud, that it may give seed to the sower and bread to the eater, so shall My word be that goes forth from My mouth; it shall not return to Me void, but it shall accomplish what I please, and it shall prosper in the thing for which I sent it.
God is saying through an analogy here that, throughout the span of history—or as Solomon would say, "under the sun" (Ecclesiastes 1:3, 9, 14, etc.)—rain has always worked to produce food for mankind. In like manner throughout that same span of time, throughout all of history under the sun, God's Word has been effective to carry out His purpose. Isaiah 55 places no limitation of 1,260 days or any other. Therefore, Revelation 11:3 cannot refer to a limited period of time when God empowers the Old and New Testaments to be effective because God's Word is always effective.
Let us not belabor the point. A careful textual analysis makes it clear that the preponderance of the language of this passage points to the Two Witnesses being individuals, not collections of books.
Who the Two Witnesses Are Not