Every time that a man has, with a pure heart, called upon Osiris, Dionysus, Buddha, the Tao, etc., the Son of God has answered him by sending the Holy Spirit. And the Holy Spirit has acted upon his soul, not by inciting him to abandon his religious tradition, but by bestowing upon him light — and in the best of cases the fullness of light — in the heart of that same religious tradition. … It is, therefore, useless to send out missions to prevail upon the peoples of Asia, Africa or Oceania to enter the Church.

Section 8 - Letter to a Priest (1951)