Although he was never himself a sillonnist, the young Joseph Cardijn, later to become the founder of the Jeunesse Ouvrière Chrétienne (JOC)or Young Christian Workers (YCW) movement, was greatly influenced by the Sillon.
Writing to a friend while studying at the University of Louvain in 1906-07, Cardijn lambasted most of his teachers for their lack of initiative. "It hurts me ... that they don't launch a movement like the Sillon".
Thus, during the summer holidays of 1907, with the assistance of one of his professors, Victor Brants, Cardijn set out himself to visit France where he met various social action leaders including those of the Sillon. He participated in a meeting of the Sillon at Lille and attended a sillonnist public meeting at Amiens where he heard Marc Sangnier defend the autonomy of a lay movement vis-à-vis the hierarchy of the Church.
It therefore seems unlikely to have been a mere accident that a couple of weeks later Cardijn would be recalled by Cardinal Mercier in Brussels - and banished to teach Latin in a Belgian country parish!
Georges Guérin, former sillonnist and founder of the French YCW with Joseph Cardijn in the early 1930s
Later after World War I, when a rehabilitated Cardijn had become director of Catholic Social Work in Brussels, Marc Sangier became the first "international lay apostle" that he would invite as a speaker.
On his return to Paris after their meeting in February 1921, a deeply moved Marc Sangnier would write, "Fr Cardijn's words of welcome were completely filled with the purest spirit of the "great times of the Sillon... Truly, I felt as if I was in the most intimate group of comrades. And I thought of Warsaw and even Lithuania where I had met similar groups of longstanding sympathy ... who identified themselves equally directly to the magnificent flowering of moral and social life of our old Sillon".
Stefan Gigacz, The Sillon and the YCW, in First Steps to a History of the YCW, International Cardijn Foundation, Brussels, 2000 at pp. 3-52.
Joseph Cardijn, Discours de bienvenue à Marc Sangnier, 5 février 1921. (French version)
Welcome to Marc Sangnier, 5 February 1921 (English translation)