To reason about Islam, do not use the Koran and Allah, because the Koran is structured to be hard to understand. Instead, use the Sunna of Mohammed. The Koran says 91 times that Mohammed is the perfect Muslim and he is very easy to understand. We find Mohammed in his traditions, the Hadith, and his biography, the Sira.
When we use Mohammed to explain Islam, we do what the Koran commands. Every hadith that I use is called Sahih (authentic), since I use Bukhari and Abu Muslim.
Sometimes you meet a Muslim who rejects all of the Sunna, so how do you use Mohammed? Simple, the Koran by itself cannot be understood by any person, without knowing the life of Mohammed. No Mohammed equals no understanding of the Koran.
The Koran is the perfect, exact words of Allah. However, the perfect Koran cannot be understood without knowing Mohammed. However, the life of Mohammed and his traditions were written by people who never met him, but wrote down what they heard from others. In a court of law, this is called hearsay. Hearsay is not admissible in our courts. So the perfect book cannot be understood without evidence that cannot be used in our courts. Odd, isn’t it?