It is true that Arabic speaking Christians use the word "Allah" for God. Simply because Allah just means "God". If we have a man called John Smith, and I tell you that he is married with children you learn something about him. If someone else tells you John Smith is single with no children, what would you conclude?
We see the same thing when we compare the Bible with the Qur'an.
[Jesus asked] "why do you call it blasphemy when I say, ‘I am the Son of God’?" (John 10:36)
The Bible says, “but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name.” (John 20:31).
O People of the Book! Commit no excesses in your religion: Nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) an apostle of Allah, and His Word, which He bestowed on Mary, and a spirit proceeding from Him: so believe in Allah and His apostles. Say not “Trinity” :desist: it will be better for you: for Allah is one Allah. Glory be to Him: (far exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs. (Surah 4:171)
And behold! Allah will say: “O Jesus the son of Mary! Didst thou say unto men, “Worship me and my mother as gods in derogation of Allah”? He will say: “Glory to thee! Never could I say what I had no right (to say). Had I said such a thing, thou wouldst indeed have known it. Thou knowest what is in my heart, though I have not known what is in thine. For thou knowest in full all that is hidden.” (Surah 5:119)Jesus clearly says he is the Son of God, the Qur'an denies this. Both cannot be true. Notice also, that the claim is that Jesus asked us to worship his mother, which is not Biblical anyway.
So clearly Allah and Jesus are very different - they cannot be the same God.
Furthermore, a cursory reading of the New Testament shows Jesus was crucified, died and was raised from the dead. The Qur'an denies this:
And because of their saying: We slew the Messiah, Jesus son of Mary, Allah's messenger - they slew him not nor crucified him, but it appeared so unto them; and lo! those who disagree concerning it are in doubt thereof; they have no knowledge thereof save pursuit of a conjecture; they slew him not for certain". (Surah 4:157)Ancient Jewish and Roman records also record the crucifixion of Jesus, which means the Qur'an stands in opposition to both the Bible and secular history.
Furthermore the Qur'an goes so far as to claim to confirm the Bible.
He sent down to you this scripture, truthfully, confirming all previous scriptures, and He sent down the Torah and the Gospel. (Surah 3:3)So for the Qur'an to be true, the Bible must be true. But if the Bible is true, the Qur'an cannot be true. Therefore, whichever way we look at it, Islam is a false religion.
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