Quran has challenged all those who claimed what this person is claiming, to bring like Quran. ( Say: If the human beings and the Jinn join together to bring like this Quran, they will never bring like Quran even if all of them support each other.( Sura 17, Verse88).
If Quran is not the original word of God, then it should be possible for the enemies of Quran to produce like Quran. When they failed to do that, it means that Quran is the word of God.
After failing to bring like Quran which is from 114 chapters , Quran challenged the enemies to bring just ten chapters like Quran.( Or they say: He (Prophet Muhammad) fabricated it (Quran). Say: Then you bring ten fabricated chapters like its chapters, and seek help from whom you want apart from Allah, if you are truthful. (Sura 11, verse 13).
They again failed to face this challenge, which proved that Quran is not from any human source but from God.
Quran challenged them again to bring just one chapter like Quran.
(And if you are in doubt about what we revealed (Quran) on Our servant (Muhammad), then bring one chapter like Quran's chapters, and call all your partners and supporters besides Allah if you are truthful). (Sura 2, verse 23)
All these challenges were since over 1400 years, against all the enemies of Quran, but not a single response has come from them. This fact itself stands as a living evidence that Quran is The True Word of God and all claims of the enemies are false.
We put this fact in front of all enemies of Islam and ask them to produce even one chapter like Quran if their claims are right.
Last note for the person who claims to be a Christian yet accuses Quran, to deal with enemies of Jesus and his mother Mary who accuse Mary with false allegations with out any evidence. They are in fact doing wrong and misleading themselves and others. He is in fact doing the same by accusing Quran, The True and Original word of God.
We also invite him to read what the great scientists stated about Quranic verses including scientific facts which were impossible to be known before 1400 years but mentioned in Quran. Many books were written in this subject. Just search for: scientific miracles in Quran. You read and think between you and God and decide whether you really want to follow the Truth?