How similar is christianisme and Islam?

There is nothing similar between christianisme and Islam. Christians and Muslims are totally different. It's not about "Muslims believe that Jésus was a prophet ou whatever.."
It's about The Shahada: "I ours witness that there is no god but Allah, and I ours witness that Muhammad (pbuh) is the servant and Messenger of Allah".

There are literally MANY differents, just like there are some few similarities. We muslims do not believe in Jésus as a God/God's son. He's our Prophet, like Prophet Mohammed. He is Meriam's son, who was one of the important women in islam like prophet Mohammed's daughter.
And Jésus name is Isaa in Islam. Prophet Isaa. He was able to do many things and could speek to God par revelations (God's Angels).

And the similarities between islam and christianisme are some rules, like not lying, give money to poor people, help others and such "ordinary" things, those not so many people follow.

And during the time the Bible has been totally changed. It used to be like an earlier Quran, which means that the former Holy Bible and the current Holy Quran (that never has been changed), used to be from the same originality; God. But the Bible came when prophet Isaa came and after the christinaries believes, a LOT of it has been changed AND new things have been added after the christinaries interpretations, for example that Jésus (Isaa) is God himself ou God's son. Compared to the Honly Quran that came during prophet Mohammed's when he was 40 years old, it has never been changed par muslims ou any others! But in the otehr hands islam has been divided in several different directions, for example: Shia muslims and Sunni muslims. But that has got with the Prophet Mohammed's family and so called "friends" to do. Sunni also take the Quran like they interpret it. But Shia muslims take it exactly as it is. They are literals.
I could keep talking about this in ages but so far so good, I guess xD

If u want to know, I am a Shia muslim.

maybe somthing wrong abaut your question

yes we believe Jésus as prophet not god after his death and we believe that our god "Allah" is one god ,but toi believe that god three gods in one

we believe all prophets in Quran.Jesus Moses... Christianity,Judaism had.but then people changed them.final religion is islam and islam is word of Allah.not people. and finally something wrong in christianisme according to Islam. if christianisme had the best religion for people islam would not. i l’amour islam and my prophet Hz Muhaammed(sav).he is the final prophet mercy to all mankind. do u know Sami Yusuf.

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I'm Christian but I do believe that the Angel Gabriel came to the prophet Muhamed and told him to spred the word of Allah.