Let us pray the prayer of St. Francis Xavier for the Conversion of Infidels
Raccolta ed. 1910, # 17, Pope Pius IX, 1847. (from the word infidelis = unfaithful):
ETERNAL GOD, the Maker of all things, remember that the souls of unbelievers have been created by Thee, and that they have been made after thy own image and likeness. Behold, O LORD, to thy dishonour, with these very souls hell is filled.
Remember, O GOD, that for their salvation thy SON JESUS CHRIST underwent a most cruel death. O LORD, suffer not that thy SON be despised by unbelievers; but, appeased by the prayers of holy men and of the Church, the Spouse of thy most holy SON, remember thy own pity, and, forgetting their idolatry and their unbelief, bring to pass that they may at length acknowledge thy SON JESUS CHRIST, who is our salvation, life, and resurrection, through whom we are saved and set free; to whom be glory from age to age without end.