John said that the Antichrist is someone who does not believe that Jesus is the Christ. Christ is an English translation of the Greek word for Messiah. The Jews did not and do not believe that Jesus is the Messiah. There were no Muslims in Johns time ao the people who received his letter would not have thought of anyone else in connection with a Messiah apart from the Jews of their day. References to Hagar and Ishmael in the Bible are in connection with the Law not with a religion that appeared some 600 years after the New Testament was written.
Of course there were believing Jews in the early church. Every leader of the Jerusalem Church was Jewish up until 70 AD
Jewish believers were still active in the Church as a whole in the time of Constantine and beyond. There were and still are many others who do not believe or are Judaisers. Paul spent a great deal of time opposing these people. Modern Judaism
is the direct descendent of the Pharisees. When they speak of the Law,(Torah) they do not have the five books of Moses in mind but the Talmud which they believe to be Oral Torah that was put in writing centuries ago. Judaism revolves around the Talmud which includes traditions condemned by Jesus and Blasphemous statements regarding him.
Of course there were believing Jews in the early church. Every leader of the Jerusalem Church was Jewish up until 70 AD
Jewish believers were still active in the Church as a whole in the time of Constantine and beyond. There were and still are many others who do not believe or are Judaisers. Paul spent a great deal of time opposing these people. Modern Judaism
is the direct descendent of the Pharisees. When they speak of the Law,(Torah) they do not have the five books of Moses in mind but the Talmud which they believe to be Oral Torah that was put in writing centuries ago. Judaism revolves around the Talmud which includes traditions condemned by Jesus and Blasphemous statements regarding him.
John refers to the great false religion as "MYSTERY" Babylon. He calls it a mystery for the very reason you cite. Islam did not exist in his day. However, the Torah/Talmud and the customs of Judaism are pretty much the same today as they were in the days of John, therefore they would not be a mystery to him.
Keep in mind also that the WOMAN of Rev 12, is Israel. This is clear by the description and context. Therefore the Harlot cannot be the same woman as the one shown in Rev 12. Also, please remember that the "Great City" of the Harlot was located in the wilderness. Jerusalem is not in the wilderness. John did not know the location because he had never been there. John knew Jerusalem well. When the Children of Israel left Egypt, where did they go and wander around for 40 years? Wilderness? Where is Mecca? Wilderness?
There are many clues about the Harlot and the 7 headed (7 historical empires) which carries the Harlot which do not fit Israel the least of which is the fact that Israel is one nation, not 7. Here are other clues that do not fit.
Conversely, Islam fits every single one of these main clues.
1.Supported by a succession of 7 (separate) World Powers throughout history
2.“Sits on”/Supported by - evil 8th Satanic Empire related to the previous 7.
3.Biggest (or oldest) False Religion on earth or both
4.Many peoples from many nations worship her
5.All nations deceived by her sorcery
6.Is also a “Great City”
7.Insults true God
8.Similar to former (original) Babylon
9.Located in a Wilderness/Desert
10.John did not seem to recognize her or her location
11.Kings of Earth fornicate (worship with) or serve her
12.Makes war with the Lamb
13.Kills Saints and Prophets
14.Beheads those who won’t convert
15.Near a busy sea (shipping) lane
16.Ships became rich from selling her “goods”
17.Merchants of the Earth weep at her demise
18.They mourn by throwing dust on their heads
19.Will be attacked and destroyed by the 8th Kingdom who carries her
20.Will be utterly burned with fire (nuked?)