Anyone who has actually studied both Islam and Christianity knows how radically different they are to each other. It has rightly been argued that Islam is less a religion and more a political ideology. This is a movement which is all about global hegemony, not just in spiritual terms, but in political terms as well.
I have already penned a piece examining the major doctrinal and theological differences between these two leading world religions: https://billmuehlenberg.com/2013/03/18/islam-and-christianity-major-differences/
So here I will focus more on the differences in terms of political, cultural, and social issues. In very brief and outline form, the contrasts are here provided:
Expansion of the faith
For the most part, the first three centuries of growth in Islam was accomplished by the use of the sword. That is, conquest and compulsion were the main means by which Islam spread throughout the Middle East in its early centuries. And much of its later expansion was based on conquest as well, with most of North Africa and the Middle East now under Islamic control mainly because of military conquest, not willing conversions. This is in accord with the example of Muhammad and injunctions from the Koran and the hadith.
During the first three centuries of the spread of the Christian church, the preaching of the gospel and the work of the Spirit combined to win many converts. The early church was often the enemy of the State, and had no official power or access to arms to force conversions. For the most part, people became Christians willingly and voluntarily. Yes, later on, Christians sometimes used the sword to force Christian conversion, but this was against the clear teachings of the New Testament.
Conversion and apostasy
In most Islamic nations today, Christians are encouraged to convert to Islam, but Muslims are strongly forbidden to leave Islam. It is law in many Muslim countries for a Muslim who apostasies to be put to death. Islam means submission, or surrender, and all people are expected to submit to Allah. In Islamic countries, Christians may freely convert to Islam, but never the reverse.
While some Christian cults and sects may have threatened their followers with death if they apostasised, that is not the biblical teaching on the matter. Church discipline, including excommunication, is enjoined on those who do not conform to right living and right beliefs, but not death. We can only pray for those who backslide; we are not to use force to bring them back.
Church and State
There is no separation of church and state in Islam. The two are one. State power and religious power were fused from the beginning. Thus almost all Muslim states today are theocratic. Sharia, or holy, law dominates every aspect of life. The only states that show some smatterings of democracy and freedom are those which are quite secular. Turkey has been an example.
In strict Muslim countries such as Saudi Arabia, Islamic law is dealt out with full force. For example, pickpockets have their hands chopped off (as Sura 5:38 commands). Or consider women who are stoned to death in places like Nigeria because they were raped (but accused of fornication).
While church and state have at times been wed through church history (e.g. Calvin’s Geneva), the modern norm is a complete separation of the two. They may be two swords in God’s hands (as Luther put it) but they have their distinct and separate roles to play. The church has limited influence over the state, while the state (in theory) is to be neutral in regard to the church. This is the case in most Western democracies.
If anything, today most Western nations push things way too far the other way, either outlawing some religious activities, or violating Christian conscience, or relegating religion to a purely private level. Thus we now have the “naked public square” to use Neuhaus’ phrase. Radical secularisation, not fundamentalism, is the biggest problem found in most modern Western nations.
Democracy and freedom
Following from the above, democratic Muslim states are quite rare, and are almost a contradiction in terms. Where Islam seems to be the strongest, and where the Koran is followed the closest, there the likelihood is that freedom and democracy will be hard to find.
Democracy exists in quite limited forms in some Muslim countries. But if democracy is defined as the situation wherein peaceful changes in government via free elections take place, only a few nations such as Turkey really qualify as a democracy. That is one or two out of some 54 Muslim states.
It has been one of the strengths of Western democracies to allow the maximum amount of democratic freedoms, while working with a rule of law. Liberty is often going to excess (libertarianism) in many Western countries today, but freedom is as commonplace in the West as it is absent in the Muslim world.
Modern Western democracies are in large measure the result of the Judeo-Christian worldview. They may be imperfect, but the human rights and freedoms found there are the greatest in the world. And without the Judeo-Christian heritage, the West as we have it today would not exist.
Muslims to this day bring up the Crusades as part of their dislike and rejection of Christianity. And they are right in some ways to do so. The Crusades were to some extent a stain on Christian history. In 1095 Pope Urban II called the first Crusade. In July 1099 they took Jerusalem, after a bloody battle. Six more crusades happened till 1291. Yet Muslims have engaged in many of their own massacres and have yet to acknowledge them or apologise for them. If the Crusades were an aberration for Christianity, warfare and jihad are mainstays for Islam.
There was a mixture of religious and secular motivations in the Crusades. Many wanted to reclaim the Holy Land from the Muslims and reclaim Christian Europe. But at times there was the desire for adventure, to get wealth, to leave home and head out on a new life. And some were bloodthirsty and just liked to kill. But others had highly righteous motivations. So it really was a mixed bag. Today most Christians apologise for the Crusades and admit that they were mainly a mistake. The New Testament gives no warrant for such activities today.
Jihad and Holy War
The term jihad has been the subject of debate. While it can just mean ‘to struggle,’ it certainly also has a much more specific designation according to Islamic jurists and the key Islamic religious texts: the call to war against the infidels. If a Muslim kills someone in the name of Allah, one could rightly argue that he is acting according to his religion. The concept of holy war can clearly be found in the Koran and hadith. Many suras speak of waging battle against the infidels or idolaters (e.g., 9:5, 29; 2:190-191; 47:4; 48:29).
Today in many parts of the Muslim world, Muslims are waging war against Christians, often with terrible massacres and violence. This is either supported by the State, or the State seems to turn a blind eye to it. Christians exist as second class citizens, or dhimmies, in most Muslim-majority nations. There is no Muslim version of “love your enemies, and pray for those who persecute you” (Matt 5:44) or of turning the other cheek (Matt 5:39).
While the Bible does have a tradition of holy war of sorts, it is restricted to the Old Testament, when Israel was commanded by God to take Canaan, and destroy its inhabitants. This was not an arbitrary or unjust conquest however. Scripture and history make it clear that the Canaanites were polluted by the grossest of immorality and violence, including child sacrifice. Their wickedness had reached a head, and the only just option was their eradication (Gen. 15:16). It was a unique, one-off affair for ancient Israel only.
If a Christian kills someone in the name of Christ, he is most certainly acting against the clear teaching of the New Testament. However, both Christian and non-Christian tradition over the centuries has developed what is known as Just War theory. This is much different from holy war. It has many checks and balances, and is usually enjoined only for self-defence, or toppling aggressive tyrannies oppressing the innocent. The war to stop Hitler and the Nazis is a primary example of this.
Numerous tragedies have been committed in the name of Islam. September 11 and the Bali bombings are just some of the more recent examples. But plenty of older examples can be mentioned, such as the bloody conquest of Constantinople in 1453, or the slaughter of perhaps 200,000 Christian Armenians by Turkish Muslims in 1894-96, because they did not convert to Islam. Muslims who carry out such activities have plenty of passages in the Koran to appeal to. In sum, it can be said that Islam is a religion of judgment, not mercy, and this has far too often been reflected in Islamic history.
Christian history certainly has cases of excesses, mistakes and aberrations. The main candidates often raised are the Crusades, the Inquisition, and the Salem witch hunts. All three are to be regretted, and none can easily be defended, although much more can be said about all three. But most thoughtful and sensitive Christians have recognised that the best policy is to acknowledge our mistakes, and to admit that often we were wrong in many ways. Moreover, there are no New Testament passages that warrant most of these things, while much of this violent religious activity can be found with approval in the Koran.
Marriage, men and women
Islam is famous for allowing polygamy (but not polyandry) as in Sura 4:3. Men have more rights than women, according to 2:228. Men are even permitted to beat women for suspected disobedience (4:34). Men may divorce their wives for any reason, while women almost never can divorce their husbands.
Islamic societies are very patriarchal, with women and children often living in fear of the man of the house. This is a reflection of how all Muslims live in fear of Allah, never knowing if they are pleasing him or not. And women are often no better than domestic servants in their own homes. The Koran and hadiths fully promote all this, with the belief that hell is populated more with women than men, and so on.
Marriage is the expected norm in Christianity, while polygamy was practiced at times in the Old Testament. Christianity revolutionised the position and role of women, declaring that men and women are equal in Christ (Gal. 3:28). While divorce rates are high in the West, biblical Christianity seeks to severely restrict it, and God says he hates it (Mal. 2:16).
Patriarchy and chauvinism are not unknown in Christian history, but they are perversions of the unity we have in Christ. Husbands are to love their wives as Christ loved the church (Eph. 5:26). Questions however remain as to the relationship between husband and wife at home, and women leadership positions in the Church, with Christians disagreeing on these sorts of issues.
These are just some of the many areas in which we can see the unbridgeable chasm between Islam and Christianity. There is no comparison between the two and those who seek to establish some sort of moral equivalence between these religions are on a futile path.