http://religion.blogs.cnn.com/2013/09/01/do-christians-muslims-and-jews-worship-the-same-god/
Final answer
So do Christians Muslims, and Jews, really all worship the same God?
In two major volumes on the subject recently published by scholars from various faiths and traditions, including Volf’s, the most inclusive response from these scholars is basically: Yes, and it’s our God.
This is not a new way of answering the question.
In 1076, Pope Gregory VII wrote this to a Muslim leader: “We believe in and confess one God, admittedly, in a different way…”
But like many other religious leaders on all sides of the argument, Gregory insisted that his version of the Almighty is the one whom the others are unknowingly and incompletely worshiping.
A less exclusivist set of religions might shrug off the differences. But all three claim to have the only “True Faith.”
So do all three faiths actually worship the same deity, whether they call him God or Allah or Adonai?
God only knows.
Jeffrey Weiss is an award-winning religion reporter in Dallas.The views expressed in this column belong to Weiss.
Catholics aren't Christians.
Catholics are actually more aligned with Muslims because they both have a works-based theology. Muslims will admit they have no guarantees for their place in eternity, that the mercy of Allah will ultimately prevail and determine their fate. In the mean time they perform works to hopefully enter Allah's paradise and will have their works weighed on scales during judgement.
Catholics also have a works-based theology that enters the equation after salvation through faith. The papacy and teaching magisterium all dictate the terms of Catholicism. It isn't fully based on scripture (more like the minutia of scripture or secondary scripture), but in oral tradition passed from generation to generation through the papacy. Catholics subscribe to the notion that the church of Rome was founded upon the apostle Peter and that each pope is an extension of Peter and that the Pope's word is law. Catholic salvation is not based upon solely upon faith, but the addition of works established by the Roman church. Catholics adhere to a sola Roma perspective, while protestants adhere to Christ and sola scriptura.
Catholics are not Christians as their salvation is not based solely through faith, but also by works; unforutnately our individual works are as filthy rags in the eyes of the Lord. It's only by the shed blood of Christ that we are saved by grace through faith in Christ and thereby justified and deemed righteous before God and indwelt by the Holy Spirit and sanctified for God's purposes. Our works cannot save us from God's judgement and wrath, but the Catholic church believes that it is so. Therefore, Catholics are not Christians and Catholics are more closely aligned with Islam because of their works-based theologies.
Makes sense to me that the papacy would make such a decree and align with Islam (even temporarily). It was in 1076 that the pope declared the supremacy of the papacy and the church even over the thrones of emperors of the time.....the papacy imposed their own standards and began to deviate from what Christ and his apostles had founded.
Even further, we witness today a great deal of Catholic converts/reverts to Islam. Catholics tired of the Roman church, but still in agreement with a works-based theology that Islam offers.