A charge to go and preach to all nations was given by Christ to His apostles.  This commission the pastors of the Church have faithfully executed down to this present time and in every age men have been raised by God and filled with His Holy Spirit for the discharge of this important function who, being sent by the authority of Christ and His name by those who have succeeded the apostles in the government of His Church, have brought new nations to the fold of Christ for the advancement of the divine honor and filling up the number of the saints.  This conversion of nations according to the divine commission is the prerogative of the Catholic Church, in which it has never had any rival.

Of all the valiant messengers of the divine Word who have, during the last few hundred years, proclaimed the good tidings among infidel nations, there is not one whose glory is greater, who has worked greater wonders or who has shown himself a closer imitator of the first apostles than the modern apostle of the Indies, St. Francis Xavier.  He labored only ten years in the missions before he was taken to heaven.  And what years they were!  In so brief a time, this one man, animated by God in a most extraordinary way, won for Christ some three million souls.

Read more at:

http://www.olrl.org/lives/xavier.shtml

Who are the best prospects for conversion? Listen to  St. Vincent Ferrer (1350-1419): "For whoever will proudly dispute or contradict, will always stand without the door. Christ, the master of humility, manifests His truth only to the humble, and hides Himself from the proud."

Pope St. Gregory the Great (590-604): "No sacrifice is more acceptable to God than zeal for souls."