39 This, Venerable Brethren, is the doctrine of the Church, which alone in the social as in all other fields can offer real light and assure salvation in the face of Communistic ideology. But this doctrine must be consistently reduced to practice in every-day life, according to the admonition of St. .James the Apostle: "Be ye doers of the word and not hearers only, deceiving your own selves." The most urgent need of the present day is therefore the energetic and timely application of remedies which will effectively ward off the catastrophe that daily grows more threatening. We cherish the firm hope that the fanaticism with which the sons of darkness work day and night at their materialistic and atheistic propaganda will at least serve the holy purpose of stimulating the sons of light to a like and even greater zeal for the honor of the Divine Majesty.
Source: Divini Redemptoris (Vatican.va)