79 Some would regard these hopes as vain flights of fancy. It may be that these people are not realistic enough, and that they have not noticed that the world is moving rapidly in a certain direction. Men are growing more anxious to establish closer ties of brotherhood; despite their ignorance, their mistakes, their offenses, and even their lapses into barbarism and their wanderings from the path of salvation, they are slowly making their way to the Creator, even without adverting to it. This struggle toward a more human way of life certainly calls for hard work and imposes difficult sacrifices. But even adversity, when endured for the sake of one's brothers and out of love for them, can contribute greatly to human progress. The Christian knows full well that when he unites himself with the expiatory sacrifice of the Divine Savior, he helps greatly to build up the body of Christ, (67) to assemble the People of God into the fullness of Christ.
Source: Populorum Progressio (Vatican.va)