Bismillah Al Hamdulilah was Salat wa Salam ala rasoolulah. Maa baad:
Allahu Alim.
In the Name of Allah, I praise Allah and thank Him and ask for His Peace and Prayers upon Muhammad, and all of the prophets of Allah, ameen. To continue:
It is only Allah Who has all the Knowledge, and we only have what He might give us.
The Holy Quran is quite clear on this subject. First of all, Allah says that the ONLY religion that He is going to accept is ISLAM [3:19].
Allah also says that if anyone desires any religion other than Islam, they will be amongst the loosers in the Next Life [3:85].
And He says that He perfected the Deen (Way of life and religion) for us and conferred His Favor upon us and selected Islam as our Deen (Way of life and religion) [5:3].
When He revealed the pure religion of worshipping only One God to the earliest of people, they were ordered to worship Allah alone, keep religion pure for Him and establish prayer, pay charity and that was the true religion. [98:4&5].
The Catholic religion is actually a composite of the early Christian religion and the Pagan Sun Worshippers religion which joined together under the leadership of the Emperor Constantine in the year of 325 on the Christian calander. Many things were introduced at that time which were never before a part of the Christian religion. Examples include the sun calander (they had always used the moon calander the same as the Jews and the one Muslims use today); changing the day of worship from Saturday to Sunday; Trinity (because Emperor Constantine ruled Rome with a Triune government); Easter; Day of Jesus birth was changed to be in keeping with the worship of the winter solstice; Communion or Holy Eucharist was introduced (this is eating bread which represents eating Jesus body and drinking wine which represents drinking his blood); the Bible was changed and compiled together as 72 or 73 books (now the Protestant Bible has only 66 books); and many other things never before a part of the Christian faith.
So, this is not the religion that Allah ordained for them nor is this the Book that Allah speaks of with reference to them following it.
Our Blessed Prophet Muhammad, peace be upon him, said that if Moses were alive today that he would have to follow the legislation (laws) which Allah had revealed be sending him (the prophet) and the Quran.
Additionally, he said that when our prophet Jesus, peace be upon him, returns he will also follow the same laws and teachings as were being revealed at the time of Muhammad, peace be upon him.
This explains why Allah revealed the Quran and now He preserves it for all the humans to know the truth of the Only Religion that He will accept.
I hope that this explains the answer to your question sufficiently, inshallah.
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Again, it is only Allah who has All Knowledge. May He forgive me my mistakes and guide us all to the right way, ameen?
Jazakalah khair and may Allah continue to guide you, ameen.
Wa As-Salam alaykum wa rahmatulah wa barakatah,
Your Brother in Islam,
Yusuf Estes