You’re all wrong, every one of you! Or…
The problem with questions about religion is that insiders have different answers than outsiders, and neither group often understands the Whys of their own answer. Actually, it’s even more complicated than that, because there’s always more than one kind of insider in any given religion. Ultimately, you could ask 6 different people (say, a militant atheist, an agnostic professor of Christian history, a Roman Catholic, a Russian Orthodox Christian, a Quaker, and an Anglican) the same question, and you’ll get 6 different answers. Which one’s right? All of them? Any of them? You just can’t think of questions of religion as having concrete answers, even one as apparently simple as yours.
Even if some genius could take all this into account and give you a complete, unbiased answer, that answer will be loooong, book-style. @Qingu is right to point out the simplification of others’ statements, but his/her statements are greatly simplified, too! Don’t fool yourself into thinking anyone here can answer your question fully. Keep your ignorance in mind, and you’ll be fine.
Now, I notice that the answers here are different from what I learned in my first-year World Religions course. I don’t know who’s right, but I’ll tell you what my prof. told me:
The primary native culture of pre-Islamic Saudi Arabia was tribal, nomadic, and pagan. The worldview was fate-based (meaning, your lot in life is due to blind senseless destiny, not your personal merits or free will) and existential (not in the capital-E sense, but in the sense that the afterlife is insignificant: what you see is what you get). Tribal ties, ancestry, and the virtue of manliness (i.e. strength, courage, self-sufficiency, honesty, helpfulness to the weak, and fame or renown amongst the people) were huge forces in determining how to act and how to judge others. Mecca and Medina were the two major cities. Mecca was a shrine city inhabited by a major tribe, Quraysh, who were caretakers for the shrine. Mohammad was born into one of the less-prestigious families of this tribe and was orphaned. At age 25, he was employed as caretaker to a rich widow; eventually they were married, had children, and were happy. The easy life led Mohammad to contemplation, and at age 40 he had his first vision. His vision was of a new reality: a Master God, Father God, omnipotent and omniscent. He preaches to his inner circle for the next 13 years, but in 613 CE he has a revelation telling him to proclaim his mission to everyone. So, he does, insisting he’s a prophet, but his tribe dismisses him, calls him crazy and possessed: after all, he’s badmouthing everything dear to them (their ancestors, manliness, tribal solidarity) and talking nonsense (a master God, the afterlife, day of resurrection). In 619, he’s banished from Mecca. Medina, however, is having a serious problem with two warring tribes. They’ve tried everything and nothing works, so in desperation they try something new: they ask Mohammad for help. Mohammad uses this opportunity to gain power and accomplish his goals of ending paganism and centralising and unifying Arabian governance. He conquers Mecca and dies Lord of Arabia. The end.
Like I said, I’m no Islamic expert. My degree, however, was in the study of Christianity, and I can say that what you wrote about Jesus isn’t right. I’ll talk about that in another post.