We understand that both Christianity and Islam are “competing religions” in that they are not mutually going to exist together. What one says to do, the other prohibits. These kinds of problems will make it impossible for them to mutually co-exist. They may both exist, but there will always be conflicts between them.
One the most important things is to strike an allegiance to an authority, the Bible or the Koran. While the Koran admits that the Bible is a holy book of God, the Bible gives no acknowledgement much less endorsement or authority to the Koran.
When we compare the two, there are counter claims that strike the one against the other. In this case, the Bible strikes against the Koran’s claims, especially as to what makes a person a prophet of God.
We start by seeing what God says in the Bible.
Deut 18:21 And if thou say in thine heart, How shall we know the word which the LORD hath not spoken? Deut 18:22 When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.
This is a simple principle. For a man to be a true prophet of God, he must speak for God, and in this capacity, he must be accurate in his predictions. In his own personal opinions, he may err freely as we all do, but when he pretends to speak God’s words, he had better be correct, or quickly retract and correct anything wrong he has said.
Deuteronomy 18:21-22 applies especially and more so to prophecies of coming doom and gloom. These prophecies typically are given by God to people who have had exposure to the truths of God, and they have rejected them or refused to live by them. God sent prophets to them to specifically condemn them, and if these prophecies didn’t get fulfilled, then the failure of the prophecy makes God look like a liar or impotent.
Qur’an 6:37-39, 36. And they said: “Why is not a sign sent down to him from his Lord?” Say: “Allâh is certainly Able to send down a sign, but most of them know not.” 38. There is not a moving (living) creature on earth, nor a bird that flies with its two wings, but are communitie like you. We have neglected nothing in the Book, then unto their Lord they (all) shall be gathered. 39. Those who reject Our Ayât (proofs, evidences, verses, lessons, signs, revelations, etc.) are deaf and dumb in darkness. Allâh sends astray whom He wills and He guides on the Straight Path whom He wills.
So the Muslim response to Deu. 18:21-22 is that the Koran itself is the sign of God as if that is enough to justify any errors in the Koran.
Heb 2:3 How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him; Heb 2:4 God also bearing them witness, both with signs and wonders, and with divers miracles, and gifts of the Holy Ghost, according to his own will?
You cannot believe the Koran and the Bible. Their principles are mutually exclusive. While the Koran commands to kill the infidel (unbeliever in the Koran), Christ says to turn the other cheek and take abuse and oppression without responding in kind. Christians today are not persecuting Muslims anywhere in the world. It is Muslims who attack, torture and kill Christians. Christians live in the spirit of Christ’s words, while many Muslims (and the majority of their religious leaders) live in contrast to these words.