The Vatican 2 document Lumen Gentium declares:
“16. But the plan of salvation also includes those who acknowledge the Creator. In the first place amongst these there are the Muslims, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge mankind.”
The first part clearly implies that Muslims acknowledge the one true God, because they profess to hold the faith of Abraham. The second part is interesting, because many Muslims actually do believe that Jesus (Mahdi) will judge mankind on the last day, but they don’t adore Him as God. Another Muslim opinion is that the Mahdi (not Jesus but someone sent by God with Jesus) will judge mankind. So what gives?
Vatican 2 implies that Muslims worship Jesus although not realizing it as they reject Him as God.
As a side note, the Koran (Qur’an) says that Jesus and Mary are sinless, but not Muhammad. The Koran also says that Jesus comes back to fight antichrist but not anti-Muhammad. My question, why is Muhammad and not Jesus the great prophet in Islam? I digress.
In the Vatican 2 document Nostra aetate (Declaration on the church’s relation to non-Christian religions), the council declared:
“3. The Church regards with esteem also the Moslems. They adore the one God, living and subsisting in Himself; merciful and all- powerful, the Creator of heaven and earth,(5) who has spoken to men; they take pains to submit wholeheartedly to even His inscrutable decrees, just as Abraham, with whom the faith of Islam takes pleasure in linking itself, submitted to God. Though they do not acknowledge Jesus as God, they revere Him as a prophet. They also honor Mary, His virgin Mother; at times they even call on her with devotion. In addition, they await the day of judgment when God will render their deserts to all those who have been raised up from the dead. Finally, they value the moral life and worship God especially through prayer, almsgiving and fasting….Since in the course of centuries not a few quarrels and hostilities have arisen between Christians and Moslems, this sacred synod urges all to forget the past and to work sincerely for mutual understanding and to preserve as well as to promote together for the benefit of all mankind social justice and moral welfare, as well as peace and freedom.”
Footnote 5 references a 1076 A.D. letter written by Pope St. Gregory VII to Anzir (Nacir), King of Mauritania (present day Algeria) (Pl. 148, col. 450f.). The relevant part of saint’s letter reads:
“Almighty God, who wishes that all should be saved and none lost, approves nothing in so much as that after loving Him one should love his fellow man, and that one should not do to others, what one does not want done to oneself. You and we owe this charity to ourselves especially because we believe in and confess one God, admittedly, in a different way, and daily praise and venerate him, the creator of the world and ruler of this world.”
The key Latin phrase “unum Deum, licet diverso modo” does not say that we worship the same God. Pope St. Gregory VII chose his words carefully. He didn’t say they believe and confess a false god or the true God. As Novus Ordo priest Rev. John L. Ubel puts it, “Pope St. Gregory VII was a skilled diplomat.” The pope was thanking the Muslim king for freeing Christian prisoners, for sending gifts, and for requesting that he (pope) send a bishop to minister to the Catholics living under Anazir’s jurisdiction. The pope’s letter was a response to the good-will gesture of a Muslim king. The pope also suggested in the letter to send two aides in hopes of establishing commercial ties. [1]
Vatican 2 implies that Pope St. Gregory VII wrote that Muslims “adore the one God.” He didn’t. On that point, Vatican 2 gives a subjective interpretation, but it’s not objectively accurate. However, is Vatican 2 right that Muslims worship the true God? In the past, I’ve argued absolutely not and that it’s one of the main heresies in Vatican 2. See Why Sedevacantism?
This article was going to reemphasize that point until I began to think hard about each argument. I thought maybe it is possible Muslims acknowledge the same God as Christianity, but with a complete misunderstanding of Him. I figured if the Apostles worshiped God but not Jesus (before they came to believe in Jesus) that by logical extension, it’s possible that God can be acknowledged but not Jesus as with Muslims.
I think the best people to answer the question are those who’ve converted out of Islam into Catholicism. Catholic convert Daniel Ali from Islam gives us the answer to the question. Daniel Ali emphatically tells that we don’t worship the same God. [2]
Conclusion
Vatican 2 and the Vatican 2 popes teach that Muslims worship the same God as Christianity.
Pope St. Gregory VII did not say Muslims and Catholics worship the same God as Vatican 2 implies. The pope said, “we believe in and confess one God,” which is a fact.
Catholic converts from Islam admit that Allah is not the same God as Christianity.
Footnotes:
[1] https://www.cathedralsaintpaul.org/sites/default/files/files/2014-09-07_weekly%20column.pdf
[2] https://www.youtube.com/watch?v=mBdG59TSDog See 15:15 to 15:23 and 17:25 where Daniel Ali repeated that we don’t have the same God.
Speray's Catholicism in a Nutshell 