Is there a good source that explains why Christian revelation is the truthful revelation and why other forms of revelation (eg. Islamic) are not? This is a question that is posed by my agnostic friends.
Vatican II’s, *Nostra Aetate * 2 says,
“…other religions found everywhere try to counter the restlessness of the human heart, each in its own manner, by proposing “ways,” comprising teachings, rules of life, and sacred rites. The Catholic Church rejects nothing that is true and holy in these religions. She regards with sincere reverence those ways of conduct and of life, those precepts and teachings which, though differing in many aspects from the ones she holds and sets forth, nonetheless often reflect a ray of that Truth which enlightens all men. Indeed, she proclaims, and ever must proclaim Christ “the way, the truth, and the life” (John 14:6), in whom men may find the fullness of religious life, in whom God has reconciled all things to Himself.”
For a book on the subject of comparative religions, I recommend *Fundamentals of the Faith * (Ignatius Press www.ignatius.com) by Peter Kreeft. You can read a chapter of his book (“Comparative Religions: The Uniqueness of Christianity.” Chapter 11) at catholiceducation.org/articles/apologetics/ap0020.html