Part (3) of the question:
It is mentioned in the Qur'an that
should be judged according to the Injil (Gospel), Surah Al-Ma'idah 5: 47?
The questioner here refers to the Ayah saying:
Let the people of the Injeel (Gospel) judge by what Allâh has revealed therein. And whosoever does not judge by what Allâh has revealed (then) such (people) are the Fâsiqûn [the rebellious i.e. disobedient (of a lesser degree)] to Allâh.
(Part No. 3; Page No. 344) This Ayah does not establish evidence for the claims of
the Christians, because the book meant here is the Injil that was revealed by Allah to `Isa (Jesus, peace be upon him) the son of Maryam (Mary, peace be upon her), not the tampered one that mentions that `Isa is the son of Allah, a god, crucified before his ascension to heaven, nor mentions glad tidings of the advent of Muhammad (peace be upon him) as a Messenger of Allah. Considering this Ayah:
And We have sent down to you (O Muhammad صلى الله عليه وسلم) the Book (this Qur’ân) in truth, confirming the Scripture that came before it and Muhaymin (trustworthy in highness and a witness) over it (old Scriptures),
this indicates that the Scriptures of Ibrahim (Abraham) and Musa (Moses), the Zabur (Book revealed to Prophet Dawud [David]), and the Injil and the Tawrah (Torah) should not be used in adjudication except for what has been authenticated, not abrogated by the Qur'an, for Allah's saying (may be He Exalted) in this Ayah:
...confirming the Scripture that came before it and Muhaymin (trustworthy in highness and a witness) over it (old Scriptures).
It has also been proven in parts (1 and 4) that both
the Jews and
the Christians have tampered with the books of their prophets. So we should, to understand the Ayahs, examine them together not individually, so that the meaning may be properly interpreted. However, those who seek deviation and deception whose hearts have been given to error, who are occupied with debate and dispute, do not take the context of these Ayahs into account or understand them separately, because
They (the disbelievers, the Jews and the Christians) want to extinguish Allâh’s Light (with which Muhammad صلى الله عليه وسلم has been sent - Islâmic Monotheism) with their mouths, but Allâh will not allow except that His Light should be perfected even though the Kâfirûn (disbelievers) hate (it).