As I understand it the main theological differences between Islam and Christianity include:
1/ The Divinity of Christ
2/ The Sonship of Christ
3/ The Trinity
4/ The means and nature of Salvation
5/ The Resurrection
6/ The crucifixion of Christ
So that has implications as to how Christians and Muslims pray.
Of the two major Islamic denominations, I'd personally say that Shi'ism has more immediate similarities in theology to my Catholic Christianity than Sunni Islam.
Ashura / Muharram, the commemoration of the martyrdom of Imam Husayn, would remind many observant Catholics of our own Good Friday / Lent (the crucifixion of Jesus), especially in terms of the mourning for the innocent wronged one side of things, and the idea of self-sacrifice.
Muharram is centred around rituals that commemorate the Shia community having been a persecuted "
under-dog" minority, alongside Christians, Zoroastrians and Jews, within the Sunni Umayyad Caliphate and their leader, Imam Husayn, suffering martyrdom for refusing to recognise (in Shia eyes) the tyrannical and unconstitutional authority of the Sunni caliphs.
Thus in the
Nahj al-Balagha, collected by
Sharif Razi, a
Shia scholar in the Tenth century, we find the following statements attributed to Imam Ali:
Letter 47
Let the eternal Reward and Blessings of Allah be the prompting factors for all that you say and do. Be an enemy of tyrants and oppressors and be a friend and helper of those who are oppressed and tyrannized.
Letter 17
We (Bani Hashim) still own the glory of prophethood (having the Holy Prophet (s) from amongst us). Prophethood which brought equality to mankind by lowering the position of mighty and despotic lords and raising the status of oppressed and humiliated persons.
I see this as somewhat reminiscent, at least in sentiment, of:
25 But Jesus called them to Himself and said, “You know that among the nations, those who appear to be their kings lord it over them, and their 'great' men are tyrants over them. 26 But it shall not be this way among you, rather whoever wishes to become great among you shall be your servant, 27and whoever wishes to be first among you shall be your slave; 28 just as the Son of Man did not come to be served, but to serve, and to give His life a ransom for many.” (Matthew 20:25-28)
"Who does not know that kings and dukes had their rulership from those who, not knowing God, strove from blind greed and intolerable presumption to dominate their equals, namely mankind, by pride, rapine, perfidy, murder, and crimes of all sorts, urged on by the ruler of the world, i.e., the devil?…"
(Pope Gregory VII in 1081: 552; see also Poole 1920: 201, fn. 5)
Thus the 'social teachings' of Christianity and Shia Islam (while very different in many other respects) do bear
some similarity, in terms of elements of social justice.
But one of the greatest differences - and it is an unbridgeable one, inasmuch as it is just a distinct outlook - has to do with the place of
divine law. Islam teaches that Allah has revealed a shariah (in the Sunnah, Qur'an and Hadith), a divinely ordained law to govern human affairs.
Christian theology repudiates this idea.
St. Paul postulated that there was no longer any objective need for a divinely imposed law for governing society but rather that the true source of "the law" was to be sought in the individual human conscience and the corresponding idea that not everyone would interpret this "natural law" in exactly the same way, meaning that difference in custom, dietary habit, clothing and civil or criminal matters had to be tolerated and could be amended in accordance with human need:
Romans 2: 14-15
Indeed, when Gentiles, who do not have the Law, do by nature what the Law requires, they are a law to themselves, even though they do not have the Law, since they show that the work of the Law is written on their hearts
Romans 14:1-23
Welcome a man whose faith is weak, but not with the idea of arguing over his scruples. One man believes that he may eat anything, another man, without this strong conviction, eats only vegetables. The one who eats meat [that isn't kosher or is sacrificed to animals] should not despise the one who refrains, nor should the vegetarian condemn the meat-eater.
Again, one man thinks some days holier than others. Another man considers them all alike. Let every one be definite in his own convictions. If a man specially observes one particular day, he does so “to God”. The man who eats, eats “to God”, for he thanks God for the food. The man who fasts also does it “to God”, for he thanks God for the benefits of fasting. The faith you have, have as your own conviction before God.
Let us therefore stop turning critical eyes on one another. If we must be critical, let us be critical of our own conduct and see that we do nothing to make a brother stumble or fall.
We should be willing to be both vegetarians and teetotallers if by doing otherwise we should impede a brother’s progress in faith. Your personal convictions are a matter of faith between yourself and God, and you are happy if you have no qualms about what you allow yourself to eat. Yet if a man eats meat with an uneasy conscience about it, you may be sure he is wrong to do so. For his action does not spring from his faith, and when we act apart from our faith we sin.
This is an enormously important idea, because in tandem with Jesus's concept of "
render to Caesar what is Caeser's and to God what is God's" and his abrogation of the ritual-cleanliness laws of kashrut and the criminal justice of the Old Testament (i.e. saving the life of the adulterous woman from being stoned to death in accordance with Deuteronomy), it moves away from the concept of prescriptive law as being of divine origin, in favour of a society in which public and private law become separate disciplines from theology, and are deemed to be fundamentally human in origin - a fallible and thus revocable human attempt to encode the intuitions of conscience for a given historical circumstance, as humankind increases in better understanding of natural law.
And that has big ramifications for the two religions.
