Becasue Allah sent books of guidance to them before the Quran. Their book is similar to the quran. other religions Allah didn't send the book for them such as buthism,. Allah is the God who send the Torah, teh Bible, and the Quran.
Islam says that Jews and Christians must be respected as People of the Book.
If you are speaking of Muslims the tern to describe Jews and Christians is Infidel or people of the book.
Christians, Jews, and Zoroastrians
Since the Muslims believe that Jews and Christians were "People of the book", they received special treatment.
Arabs refer to Christians and Jews as "people of the book," recognizing them as followers of divine scriptures (the Bible). This term acknowledges their shared belief in monotheism and the importance of revealed texts.
The term "People of the Book" refers to Jews, Christians, and Muslims who all follow religious texts believed to be revealed by God, such as the Torah, Bible, and Quran.
Muslims refer to Christians as "Ahl al-Kitab" which translates to "People of the Book" in Arabic.
people of the book أهل الكتاب
In the Quran, Muhammad referred to Christians and Jews as "People of the Book" (Ahl al-Kitab). This term acknowledges their possession of earlier scriptures, such as the Torah and the Gospel, and highlights a shared religious heritage. The Quran often emphasizes the importance of dialogue and respect between Muslims and the People of the Book.
Muhammad preached tolerance for Christians and Jews as People of the Book because they recognize the God of Abraham as the one and only god. Another reason is that Christians and Jews practice faiths that have been revealed through divine ordinances.
Muslims do not encourage their children not to like Christians. Christians and Jews are people of the book as mentioned in the Quran and the people closer to Muslims are Christians as mentioned in the Quran. Muslims are allowed to marry Christians and Jews as they are people of the book. It is therefore a misconception on your part to think that Muslims are encouraged not to like Christians!
Jews and Christians were considered the People of the Book because they had received prior revelations from God.