Christianity and Islam are the largest religions in the world. Thirty-three percent of the world's population are Christian, twenty-one percent Muslim. The world's two largest religions have much in common, but they are also different in some crucial ways. The origins of both religions are fully described in my book, Science and Technology in World History, Vol. 2.
Both Christianity and Islam are offshoots of Judaism. From Judaism, Christianity and Islam derived the doctrines of monotheism, prophecy, resurrection, and a belief in the existence of heaven and hell.
Both Islam and Christianity have a holy book. Christians consider the Bible the inspired word of God. But Muslims believe that the Koran is the literal word of God. Mohammed was merely transcribing the words of Allah, much as a court reporter does. Muslims therefore attribute greater spiritual authenticity to the Koran and Islam than to the Bible and Christianity.
In Catholicism, salvation is obtained through the sacraments of the Church, including baptism, penance, and the Eucharist. Most Protestant denominations hold the doctrine that salvation depends solely on faith in Jesus Christ. But in Islam, salvation is through works and is not limited to Muslims.
Christianity is focused on forgiveness, charity, and mercy, with a side dressing of apocalyptic visions, Hell, and the wrath of God. But Islam is centered on justice and the destruction of unbelievers. Allah is merciful -- but not to infidels. The early history of Christianity is one of persecution and martyrdom. Jesus himself submitted to crucifixion. In contrast, Islam was not born in submission and earnest entreaty, but in warfare against the enemies of Allah.
After the Hegira, Mohammed and his followers began a jihad against their pagan enemies in Mecca. At the Battle of Badr in 624 AD, Mohammed's servant found one of his master's enemies lying wounded on the battlefield. He cut off the man's head and presented it to Mohammed as a present. The Prophet was overjoyed. He exclaimed, "The head of the enemy of Allah! It is more acceptable to me than the choicest camel in all Arabia." After the bodies of his foes were cast into a pit, Mohammed stood at the edge of the pit and taunted the dead by asking, "Have you found that what Allah threatened is true?"
Consider how Jesus and Mohammed handled what was essentially the same problem. A woman who had committed adultery was brought before Jesus for judgment. As she had been caught in the very act, there was no question of her guilt. The sentence dictated by Mosaic Law was death by stoning, but Jesus showed mercy. He said, "He that is without sin among you, let him first cast a stone at her." Embarrassed, the woman's accusers dropped their rocks and walked away. Jesus told the woman to go home and repent. But when a man and a woman who had committed adultery (with each other) were brought before Mohammed, he exclaimed, "Stone them," and the pair was executed.
Christians tend to attribute greater spiritual authenticity to Christianity because of its emphasis on mercy and forgiveness. But in fact, the God of the Christians is as unrelenting as Allah in His condemnation of unbelievers. In Luke, Jesus describes how God tortured a rich man in Hell by burning him. In the parable of the wheat and the tares, Jesus proclaims that at the Last Judgment, God will send out angels to gather the "children of the wicked one" and "cast them into a furnace of fire."
No faith has an unblemished history of extending charity to the enemies of God. When Christian Crusaders captured Jerusalem in 1099 AD, they massacred the Muslims and Jews. Raymond of Aguilers claimed that "men rode in blood up to their knees and bridle reins." This was no doubt an exaggeration, but nevertheless an indication of terrible mayhem. To the atrocities committed under the banner of Christianity we could add the Inquisition, the Witch Mania, and the infamous Malleus Maleficarum (Hammer of the Witches), first published in 1487 AD.
The roots of Christian charity lie in the ethics advocated by the Hebrew prophets. But the Jews also killed the enemies of God. In the book of Deuteronomy, God gave the Hebrews license to destroy their enemies and plunder their cities. "Thou shalt smite them, and utterly destroy them; thou shalt make no covenant with them, nor show mercy unto them."
We know more about Mohammed than Jesus because the latter was recognized during his lifetime as the founder of Islam. Thus, there were contemporary biographies and written records. In contrast, no one recognized Jesus as an important person in his own lifetime. Even as late as fifty years after his death, Jesus remained nearly a complete unknown to the Mediterranean world. Our primary sources for the life and teachings of Jesus are the Gospels. And the Gospels were never intended to be objective historical documents. They were written to proselytize. The author of John explains that "these are written so that you may believe."
In the West, religion is largely treated as a matter of conscience, and there is a tradition of freedom of religion. But Islam is a way of life, not just a personal belief. Individual behavior is specified in the Koran. Gambling and the consumption of both pork and alcohol are forbidden. Slavery is allowed, but slave owners are admonished to treat their servants well. Fornication is punishable by scourging. To allow individual transgressions would undermine the moral fabric that binds Islamic societies together.
Perhaps no aspect of Islam is more misunderstood by Western Christians than its role in government. Jesus began a tradition of divorcing Christianity from secular government by declaring that people should not confuse secular and spiritual obligations. "Render therefore unto Caesar the things which are Caesar's, and unto God the things that are God's." Jesus also said, "My kingdom is not of this world."
But there is no tradition of separating government and religion in Islam. Indeed, such a separation would likely strike a Muslim as insane. Government exists to enforce moral rules of behavior, and morality is defined by religion. The two are therefore inexorably intertwined.
Government in Islamic countries is necessarily theocratic. The Koran is a handbook for an entire system of government. In Life of Mahomet, William Muir explains, "Scattered throughout ... [the Koran are] ... the archives of a theocratic government in all its departments ... The elements of a code both criminal and civil are ... introduced. Punishments for certain offences are specified, and a mass of legislation laid down for the tutelage of orphans, for marriage, divorce, sales, bargains, wills, evidence, usury and similar concerns."
Westerners seem oblivious to the fact that not everyone in the world believes in the superiority of democratic government. The Greek system of democracy is foreign to Islam. Muslims no more appreciate having a democratic government forced upon them than Westerners would like being forced to live under an Islamic theocracy.
Women have an inferior status in both Christianity and Islam. Genesis states that God first created Adam. Eve was sort of an afterthought, manufactured purely to be a helper and companion for the man, Adam. And it was the scheming Eve who created original sin by talking the guileless Adam into eating the forbidden fruit. St. Paul forbade women to speak in church and instructed them to submit to their husbands. According to Paul, the man was not "created for the woman; but the woman for the man."
In Sura 4, the Koran plainly states that "men are superior to women." Women are instructed to dress modestly. A "virtuous" woman is one who is "obedient." If she is not obedient, her husband is allowed to scourge her. But the husband is admonished not to punish a virtuous woman.
God does not speak to me, so I cannot make any substantive comment on the degree to which any religion may be correct or incorrect. However, no matter what our personal beliefs are, it is important that we recognize the significant differences between Christianity and Islam.