Why Did the Vatican Clarify Mary's Role in Salvation History?

Through the Dicastery of the Doctrine of the Faith, the Vatican recently published a document called "Mater Populi Fidelis," or "Mother of the Faithful People of God," which clarifies different titles for the Blessed Virgin Mary. Father Dave explains the purpose of this document, specifically in reference to the Vatican's rejection of labeling Mary "co-redemptrix" or "co-mediatrix."