64 If, as We said, the Church realizes what is God's will in its regard, it will gain for itself a great store of energy, and in addition will conceive the need for pouring out this energy in the service of all men. It will have a clear awareness of a mission received from God, of a message to be spread far and wide. Here lies the source of our evangelical duty, our mandate to teach all nations, and our apostolic endeavor to strive for the eternal salvation of all men. Merely to remain true to the faith is not enough. Certainly we must preserve and defend the treasure of truth and grace that we have inherited through Christian tradition. As St. Paul said, "keep that which is committed to thy trust." (42) But neither the preservation nor the defense of the faith exhausts the duty of the Church in regard to the gifts it has been given. The very nature of the gifts which Christ has given the Church demands that they be extended to others and shared with others. This must be obvious from the words: "Going, therefore, teach ye all nations," (43) Christ's final command to His apostles. The word apostle implies a mission from which there is no escaping. To this internal drive of charity which seeks expression in the external gift of charity, We will apply the word "dialogue."
Source: Ecclesiam Suam (Vatican.va)