What is the reason for mentioning the permissibility of the food of the People of the Book for Muslims in Surat Al-Ma'idah, "The food of those who were given the Scripture is lawful for you and your food is lawful for them," and is the statement that this is a reward for them correct?

The text of the verse from Surah Al-Ma'idah states: "And the food of those who were given the Scripture is lawful for you." What is meant by "food" here are the slaughtered animals of the People of the Book, as interpreted by Ibn 'Abbas. Allah permitted to Muslims the lawfulness of the slaughtered animals of the People of the Book and marrying their chaste women. He also permitted them to eat our food, but it is not permissible for our women to marry them, by scholarly consensus. There is no difference between a Person of the Book and other disbelievers in commercial dealings such as rice, cars, and so forth.