"I think that Islam and Christianity are the most closely related religions than they are to any other religion (Judaism comes in a close second)."
As somebody who has studied judiasm, Christianity, and Islam in depth I strongly disagree with you.
Islam is mostly a hodgepodge of the pagan religion that existed in Muhammads time (the 5 pillars of islam were part of this), it also took elements from Zorasterism (ONly one god and muhammad his prophet is very close to what Zoraster and said about his god, verbatum except the name of the god was different and each individual claimed themselves as his prophet. Characters such as Jesus, Mary, Moses, and others are essentially taken mostly in name only and given completely different stories found in the Judeo-Christian tradition.
Islam is more deeply influenced by the pagan religion of Mecca than Christianity. Islam's monotheism comes from Zoraserism and Christianity and thats about it.
As well, the Tanakh and New testament are considered curropted by the Jews and Christians so while they may read the Bible anything that doesn't jibe with Islam is disregarded. So even when Muslims and Christians do read the same texts from the bible they have radically different perpectives on what they read.
Fuck it, I'll just come out and say it, Muhammad was a sick phedophile, whole broke the rules of even his own religion (he had like 12 wives when his religion calls for 4. I will give him the progressive act of legalizing prostitution though by allowing temporary marraiges. Married Aisha at 6, consomating his marrage with her when she was 9. He was a racist hating blacks, called for the death of many jews, killed poets who revealed him for the charleton he was. Muhammad used his religion as a tool to gain money, sex and power. Muhammad united the arabs by military conquest.
The message of Jesus was different. He chose peace. It's actually interesting, one of my old professors told us of one of his old professors suggesting that when Jesus was giving the Sermon on the Mount/Plain he was actually giving a speech to the sicari or daggerment. They were also known as the zealots. Jesus at first may have thought about becoming the Davidic Messiah (many jews in Jesus' time believed in 2 or possibly 3 messiah's coming to help them in time of need, one a preacher, one a warrior. THe davidic messiah would be the warrior obviously). Remember when he said "I come not to bring peace but the sword" more or less. I am paraphrasing out my ass but you know what I mean. Jesus, however, decided to chose peace.
Oh and I am an athiest/agnostic...it depends on what side of the bed I wake up on in any given day.