Was not this doctrine invented in 1870?

No. Papal Infallibility was promulgated as a dogma in 1370, but the doctrine was not invented then. The Vatican Council under Pope Pius IX. merely said definitely, “This is the Christian doctrine contained at least implicitly in the revelation originally given to mankind by Christ.” This prerogative of infallibility was conferred upon St. Peter, and upon his successors, in virtue of Christ’s choice oi St Peter as the rock-foundation oi the Church, His prayer for St. Peter that his faith might not fail, His commission to him to confirm his brethren and to feed the whole flock, lambs and sheep. The Church does not say in her definitions, “I now reveal this doctrine,” but, “I definitely declare this to be the doctrine revealed by Christ.” If she never taught with such authority, men would say, “What is the good of the Church?” If she does teach with authority they say, “She is inventing new doctrines.” After all, the Catholic Church defined the “Filioque” in 1439, and you accept that without complaining that she invented a new doctrine. Why complain when she exercises the same functions in 1870? She will define other doctrines more explicitly in future times as need arises, doctrines we already believe in believing all that has been revealed by Christ, though we do not advert to the fact that these particular doctrines are certainly included. For although the definitions will be new, they will not involve new truths of religion. Now that the personal infallibility of the Pope has been defined we know that it belongs essentially to the original teaching given by Christ.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty