0 Catholic missionaries toiling in a vast field of labor "that the word of the Lord may run its course triumphantly" are in Our thoughts in a special way on the occasion of the 25th anniversary of the Encyclical Letter Rerum Ecclesiae of Our Predecessor of immortal memory Pius XI, wherein he laid down wise norms for the greater development of Catholic missions. The consideration of the progress this holy cause has made in the intervening years has brought Us no small consolation. As We remarked in an audience on June 24, 1944, to the directors of the Pontifical Missionary Work; "The Catholic missionary movement both in Christian and pagan lands has gained such force and momentum and is of such proportions as perhaps was never witnessed before in the annals of Catholic missions."
Source: Evangelii Praecones (Vatican.va)