Não sabia bem em que sub-forum colocar este artigo, e contra melhor julgamento coloquei-o aqui. Muito esclarecedor este artigo, ainda que esteja escrito em inglês.

Catholicism and Islam are monotheistic religions, that is, both believe that there is but one God. However, that does not necessarily imply that they worship the same God. Two men may be married to one woman, but that does not mean that they are married to the same woman. So, the question is whether Catholics and Muslims worship the same one God.
The modern Catholic Church has defined her relations to non-Christian religions in a document entitled Nostra Aetate. The section on Islam begins thus:
The Church regards with esteem also the Muslims. They adore the one God, living and subsisting in Himself; merciful and all-powerful, the Creator of heaven and earth, who has spoken to men.
While it does not state explicitly that 'the one God' adored by the Muslims is the true and living God, this seems to be the natural implication. For why would Rome commend Muslims for this belief if their God was considered a false deity? Indeed, unlike their ancestors, many modern Catholics are convinced that they and Muslims worship the same God.
Is this true? Is the Father of our Lord Jesus Christ the same as Allah? What does the Bible teach about God? What does the Quran say?
The True and Living God
Following the ordinance of our Lord, Christians are baptised in the name of the Father, and of the Son and of the Holy Spirit. The baptismal formula of the initiation rite reflects the Christian doctrine of the holy Trinity. The disciples are baptized in the singular name of God (for God is one), and yet, three distinct persons are mentioned, the Father, the Son and the Holy Spirit.
The biblical doctrine on the Trinity is correctly expressed in the Nicene and Athanasian creeds:
We believe in one God, the Father, the Almighty, maker of heaven and earth, of all that is, seen and unseen. We believe in one Lord, Jesus Christ, the only Son of God, eternally begotten of the Father…We believe in the Holy Spirit, the Lord, the giver of life…
Now the catholic faith is that we worship One God in Trinity and Trinity in Unity, neither confounding the Persons nor dividing the substance. For there is one Person of the Father, another of the Son, another of the Holy Spirit. But the Godhead of the Father, of the Son, and of the Holy Spirit, is One, the Glory equal, the Majesty coeternal.
These definitions were forged in the furnace of great controversies in the early church. Heretics troubled the church with false doctrines about God, especially Arius, who denied the Deity of Christ. In response, the orthodox Fathers laboured in the Scriptures to formulate the true doctrine of God. They understood the fundamental importance of this doctrine, and rightly warned that: 'This is the catholic faith, which except a man shall have believed faithfully and firmly he cannot be in a state of salvation.'
The importance of the doctrine of the Deity of Christ cannot be overstated. Unless the Son is truly God and 'one with the Father', Christians would be idolaters, for we regard Jesus as our Lord and Saviour and gladly worship him. If Jesus were not God, we would be found trusting in a creature for our salvation. But we confess that Jesus is not merely another prophet, but the Son of God. The Jews in hid day understood well what he meant by that title: 'For a good work we do not stone You, but for blasphemy, and because You, being a Man, make Yourself God' (John 10:33). They did not believe his claim to Deity and condemned him to death for blasphemy. But Christians understand his claim and believe him; we trust and worship the Son of God; we live and die for our Lord. For in Christ we know God in truth:
And we know that the Son of God has come and has given us an understanding, that we may know Him who is true; and we are in Him who is true, in His Son Jesus Christ. This is the true God and eternal life (1 John 5:20, 21).
The Son is the true God; any other god is an idol.
The Quran
Islam vehemently rejects the doctrine of God as revealed in Holy Scriptures.
Islam denies the Trinity:
Certainly they disbelieve those who say: Surely Allah is the third (person) of the three; and there is no god but the one God, and if they desist not from what they say, a painful chastisement shall befall those among them who disbelieve (Sura 5:73).
O People of the Scripture! Do not exaggerate in your religion nor utter aught concerning Allah save the truth. The Messiah, Jesus son of Mary, was only a messenger of Allah, and His word which He conveyed unto Mary, and a spirit from Him. So believe in Allah and His messengers, and say not 'Three' - Cease! (it is) better for you! - Allah is only One Allah. Far is it removed from His Transcendent Majesty that He should have a son (Sura 4:171).
Islam denies the Father and the Son:
The Christians say: The Messiah is the son of Allah; these are the words of their mouths; they imitate the saying of those who disbelieved before; may Allah destroy them (Sura 9:29-30).
It does not befit GOD that He begets a son, be He glorified (Sura 19:35).
Islam denies the Deity of Christ:
The Messiah, Jesus the son of Mary, was no more than God’s apostle (Sura 4).
They do blaspheme who say: Allah is Christ the son of Mary (Sura 5:72).
And when Allah saith: O Jesus, son of Mary! Didst thou say unto mankind: Take me and my mother for two gods beside Allah? he saith: Be glorified! It was not mine to utter that to which I had no right (Sura 5:116).
In blasphemy indeed are those that say that Allah is Christ the son of Mary (Sura 5:17).
Clearly then, the Quran denies:
1. The Trinity;
2. The Sonship of Christ;
3. The Deity of Christ.
The conclusion is inevitable: the god of Islam is not the same God of the Holy Scriptures. Christians do not adore the same God as Muslims. Muslims are not merely ignorant of the Triune nature of God and the Deity of the Son: the Quran explicitly negates the doctrine of Christ as taught in the Bible. Rather than adoring God with us, Muslims pray to their god that he might destroy us because of our faith in Christ, the Son of God. 'The Christians say: The Messiah is the son of Allah; these are the words of their mouths; they imitate the saying of those who disbelieved before; may Allah destroy them' (Sura 9:29-30).
The Catholic Position
The Roman Catholic Church upholds the doctrine of the Trinity (Catechism paragraphs 261-267). It is therefore astounding that the Catechism contradicts everything the Catholic Church has taught about God and states that Catholics and Muslims worship the same God:
The Church’s relationship with Muslims. The plan of salvation also includes those who acknowledge the Creator, in the first place among whom are the Muslims; these profess to hold the faith of Abraham, and together with us they adore the one, merciful God, mankind's judge on the last day (Catechism of the Catholic Church, paragraph 841, quoting Lumen Gentium 16, November 21, 1964).
According to the Catechism, 'together with us (Catholics) they (Muslims) adore the one, merciful God.' Pope John Paul II repeats this statement even more clearly. Addressing Muslim youths, the Pope said: 'We believe in the same God, the one and only God, the living God, the God who creates worlds and brings creatures to their perfection' (What Dialogue Means for Catholics and Muslims, US Conference of Catholic Bishops, http://www.usccb.org/seia/brunett.htm).
How could Catholics and Muslims worship the same God since Muslims deny the Trinity, the Sonship and the Deity of our Lord? Quite frankly, the statement that Catholics and Muslims adore the same God is false. I will not speculate on the motives of the modern Catholic hierarchy for making this false assertion. However, it should be evident to every Catholic who has complete confidence in the infallibility and unchangeableness of the Roman magisterium, that in fact the Vatican's teaching on this matter has changed and that it is both fallible and mistaken.
Dr Robert Reymond comments on the odd stand of Roman Catholicism on Islam:
I should note in passing that Islam’s doctrinal hostility to Biblical Christianity apparently does not bother the Roman Catholic Church, for Rome declared in its 1994 Catechism of the Catholic Church (paragraph 841) that Muslims are included within God’s plan of salvation because they 'acknowledge the Creator,...profess to hold the faith of Abraham, and together with [Christians]...adore the one merciful God [Muslims and Christians hardly 'adore' the same 'one merciful God'].' Never mind that Islam’s Allah is not the triune God of the Old and New Testaments; never mind that Muslims think our Trinity is made up of God, a human Jesus, and Mary his mother, the last two of whom we blasphemously worship along with God; never mind that they deny that Jesus Christ is the divine Son of God and that he died on a cross a sacrificial death for his people’s sin and rose again because of their justification; never mind that Muslims believe that Christians are idolaters because we worship Christ who they contend was simply a human Messiah and a human prophet; never mind that they see no need for Christ’s substitutionary atonement or for that matter any substitutionary atonement at all. According to Rome’s teaching, in spite of their unbelief, Muslims are still salvifically related to the People of God and may go to Heaven as Muslims, all of which shows how serious is Roman Catholicism’s departure from Christianity (Reymond, R. What’s Wrong with Islam?).
Christian Response
The Christian response to Muslims should be twofold. Firstly, we must separate ourselves from Islam and clearly state that it is a false religion. 'Whoever transgresses and does not abide in the doctrine of Christ does not have God. He who abides in the doctrine of Christ has both the Father and the Son. If anyone comes to you and does not bring this doctrine, do not receive him into your house nor greet him; for he who greets him shares in his evil deeds' (2 John 9-11). Christians do not have any ecumenical relationship with Muslims. We cannot participate in their idolatry by saying that we worship the same God. On the contrary, we must warn them that since they do not abide in the doctrine of Christ, they do not have God.
Secondly, we have an evangelistic responsibility towards Muslims. They have been indoctrinated against the Son of God. We must proclaim Jesus, the Son of God, the Lord from Heaven, the Saviour of the World. We must proclaim that he died for our sins according to the Scriptures, that he was buried, and that he rose again the third day according to the Scriptures. This is our message to Muslims, and to the rest of the world, 'He who believes in the Son has everlasting life; and he who does not believe the Son shall not see life, but the wrath of God abides on him' (John 3:36).