Marxism underlies the way of thinking that continues to be one of the most corrosive threats to the Church (even winding its way into the Church as liberation theology) and in 1938, when Emmanuel Mounier—who heavily influenced Jacques Maritain and Dorothy Day—wrote his seminal book A Personalist Manifesto, (it is very difficult to find a copy, but well worth the search) it was strongly ascendant.
Mounier defines personalism:
“We shall apply the term personalist to any doctrine or any civilization that affirms the primacy of the human person over material necessities and over the whole complex of implements man needs for the development of his person.” (p. 1)
And he argues that:
“Personalism is the only basis on which an honest and successful combat can be waged against Marxism.” (p. 44)
“It is this intimate life of the person, vibrant in all our acts, that is the rhythmical reality of human existence. It alone answers the need for authenticity, for true action, and for the fullness of life which Marxist materialism and fascist naturalism try to find in the objective realizations of man. Nothing can take its place.
“The error of the mathematicians,” Engels once wrote, “was to believe that an individual could achieve by himself what can be achieved only by the whole of mankind in its constant development.” We answer that the error of fascism and Marxism is to believe that the nation or the state or Humanity can and must undertake in its collective evolution what alone each human person can and must undertake in his personal development.” (p. 79)