Pope Francis is insisting that his concern for the poor and critique of the global economic system isn't some novel, communist-inspired ideology but rather the original and core "touchstone" of the Christian faith.

Some U.S. conservatives have branded Francis a Marxist for his frequent critiques of consumerism and focus on a church "that is poor and for the poor." But in an interview contained in a new book, Francis explains that his message is entirely rooted in the Gospel and has been echoed by church fathers since Christianity's first centuries.

In the book "This Economy Kills," a study of Francis' economic and social teachings, Francis says: "The Gospel does not condemn the wealthy, but the idolatry of wealth."