What is the convincing answer to a Christian's question: Why did Allah Almighty not preserve the Gospel from distortion and loss? And what are the best sources for inviting Christians to Islam in English?

Al-Ayni mentioned that Muhammad ibn al-Waddah explained to some Christian scholars the reason for the preservation of the Quran from addition and deletion, unlike their scriptures. He stated that Allah undertook the preservation of the Quran when He said: "Indeed, it is We who sent down the Dhikr (the Quran), and indeed, We will be its guardian." (Quran 15:9), whereas Allah entrusted the preservation of their scriptures to them. Al-Shanqiti clarified that Allah tasked the rabbis and monks with preserving their book, but they distorted and altered it. As for the wisdom behind Allah's preservation of the Quran alone, it lies in the fact that the Quran is the book of the enduring message until the Day of Judgment, unlike other books which were subject to abrogation, and whose preservation was entrusted to the scholars among the People of the Book.