35 All Christians all over the world must fulfill this obligation; yet it is easy to see that if it were carried out in the mission territories, it would bear special and abundant fruits, particularly valuable for extending the Kingdom of God among those who do not know the wonderful gift of our Faith and the supernatural power of grace. Thus Jesus Christ admonishes us: "Even so let your light shine before men, in order that they may see your good works and give glory to your Father in Heaven"; (61) and St. Peter exhorts the faithful to "abstain from carnal desires which war against the soul. Behave yourselves honorably among the pagans, that, whereas they slander you as evildoers, they may, through observing you by reason of your good works, glorify God in the day of visitation." (62)
Source: Princeps Pastorum (Vatican.va)