Mission - a requirement of the Church's catholicity
The missionary task implies a respectful dialogue with those who do not yet accept the Gospel. Believers can profit from this dialogue by learning to appreciate better "those elements of truth and grace which are found among peoples, and which are, as it were, a secret presence of God." They proclaim the Good News to those who do not know it, in order to consolidate, complete, and raise up the truth and the goodness that God has distributed among men and nations, and to purify them from error and evil "for the glory of God, the confusion of the demon, and the happiness of man."
Source: Catechism of the Catholic Church (Vatican.va)