For better or worse, I don't think this is Sola_Fide's point.
I don't think Sola is saying that an Arab Christian who prays to "Allah" by which he means the Christian God, but in a different language, is not saved.
What Sola is saying is that the Muslim version of God ("Allah") is fundamentally different than the true God, even if he is described as "Allah" by Arabic Christians. In other words, Sola_Fide is saying that an Arab Christian who speaks Arabic and prays to Allah is nonetheless not praying to the same God that Muslims pray to.
Acts 16
Then he came to Derbe and Lystra. And behold, a certain disciple was there, named Timothy,
the son of a certain Jewish woman who believed, but his father was Greek. 2 He was well spoken of by the brethren who were at Lystra and Iconium. 3 Paul wanted to have him go on with him. And he took him and circumcised him
because of the Jews who were in that region, for they all knew that his father was Greek. [my addition: He circumcised him not because it was mandatory or necessary, but to appeal to the Jews in that region. And take note that he was the son of a Gentile, particularly, a Greek. And the Greeks believe in a great plurality of gods with one head, and they also believed in divine-humans beings.]
4 And as they went through the cities, they delivered to them the decrees to keep, which were determined by the apostles and elders at Jerusalem. [my note: and what are these decrees but the very teachings of God in the Holy Spirit. His teachings on communal living, relationship with our neighbors, the worship and devotion towards God in prayers. And above all, communing of the Lord's Supper and Mystical Feast and celebrating His Resurrection. These are the traditions handed from the beginning and practiced since the beginning, the rituals established by decrees from the leaders of the Church in the world, namely the Apostles who were also the first Bishops of their days. This is what some call 'organized' religion].
5 So the churches were strengthened in the faith, and increased in number daily.
The Macedonian Call
6 Now when they had gone through Phrygia and the region of Galatia, they were forbidden by the Holy Spirit to preach the word in Asia. 7 After they had come to Mysia, they tried to go into Bithynia, but the Spirit did not permit them. 8 So passing by Mysia, they came down to Troas. 9 And a vision appeared to Paul in the night. A man of Macedonia stood and pleaded with him, saying, “Come over to Macedonia and help us.” 10 Now after he had seen the vision, immediately we sought to go to Macedonia, concluding that the Lord had called us to preach the gospel to them.
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If it is the calling of Pope Francis to go and preach God's love to the Muslim world, then I commend him and wish him many years.
