What error is condemned in "Gaudium et spes"?

Dr. Arthur Hippler, Director of the Office of Justice and Peace, Diocese of La Crosse, has an excellent article on this and it is quite appropriate considering the present day circumstances of professed Catholic politicians and others who are so adamant about separating their 'public' lives from their 'professed' Catholic faith.

The condemnation of error is a rare occurrence within the documents of the Second Vatican Ecumenical Council. Pope John XXIII indicated in his opening speech that the Council was quite deliberately more concerned with affirming the truth of the Faith than condemning the errors opposed to it. When therefore errors are condemned, we should take notice. For despite its generally commendatory attitude, Gaudium et spes condemns what it considers to be "one of the graver errors of our age."

What is this "graver error"? It is not liberal capitalism, nor atheist communism, nor any economic or social system. Rather, it is the root and principle of all social and economic errors. It is rather the divorce of the Catholic faith from secular life.

...This split between the faith which many profess and their daily lives deserves to be counted among the more serious errors of our age" (Gaudium et spes, n.43).

The Council Fathers make clear that this error is condemned in Holy Scripture: "Long since, the Prophets of the Old Testament fought vehemently against this scandal (cf. Is. 58:1-12) and even more so did Jesus Christ Himself in the New Testament threaten it with grave punishments (Cf. Mt. 23:3-33; Mk. 7:10-13).

"The Christian who neglects his temporal duties, neglects his duties toward his neighbor and even God, and jeopardizes his eternal salvation" (GS, n.43).

Dr. Hippler's article can be read here.