Christianity, Judaism and Islam are Abrhamic religions, all 3 hold Abraham as a somewhat important figure in their history. Christinaity believes Jesus is a decedent of Abraham while Islam views Mohammed as a decedent of Abraham. and then Jews Jacob.
Christians believe Jesus was the son, Muslims believe he was a messenger, and Jews think he was a false messenger. Truly, that is the single biggest and most notred difference between the 3. (Sunni and Shiite notwithstanding, Trinity notwithstanding).
Infact, the Qu'ran even goes so far as to say that Allah, Yaweh, and God are the same diety, and that Muslims, Jews and Chritians all believe in the same singular God.
Call it what you want, but the 3 main religions (considering they consists of 54% of the worlds religions) all believe in the same idea of the same single god with a monothestic view, and all 3 have many of the same figures, places, and events transcribed throughout their holy books, sharing many of the same ideas with eachother.
These 3 religions share much more in common than not only people know, but the extremist are willing to accept.