Finally, those who have not yet received the Gospel are related in various ways to the people of God.(Cfr. S. Thomas, Summa Theol. III, q. 8, a. 3, ad 1.) In the first place we must recall the people to whom the testament and the promises were given and from whom Christ was born according to the flesh.(Cf. Rom. 9, 4-5) On account of their fathers this people remains most dear to God, for God does not repent of the gifts He makes nor of the calls He issues.(Cf. Rom. 11, 28-29);
… then those who share belief in the same God:
But the plan of salvation also includes those who acknowledge the Creator. In the first place amongst these there are the Mohamedans, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge (hu)mankind.
The bishops remind us that God’s initiative is present among those who do not profess belief in the Creator:
Nor is God far distant from those who in shadows and images seek the unknown God, for it is He who gives to all (people) life and breath and all things,(Cf. Acts 17,25-28) and as Saviour wills that all … be saved.(Cf. 1 Tim. 2, 4) Those also can attain to salvation who through no fault of their own do not know the Gospel of Christ or His Church, yet sincerely seek God and moved by grace strive by their deeds to do His will as it is known to them through the dictates of conscience.(Cfr. Epist. S.S.C.S. Officii ad Archiep. Boston.: Denz. 3869-72.)
The living of a good life is groundwork for the Good News:
Nor does Divine Providence deny the helps necessary for salvation to those who, without blame on their part, have not yet arrived at an explicit knowledge of God and with His grace strive to live a good life. Whatever good or truth is found amongst them is looked upon by the Church as a preparation for the Gospel.(Cfr. Eusebius Caes., Praeparatio Evangelica, 1, 1: PG 2128 AB.) She knows that it is given by Him who enlightens all … so that they may finally have life.
Most troubling are those believers who have forsaken God for other gods, as well as those who have given in to a “final despair.”
But often (people), deceived by the Evil One, have become vain in their reasonings and have exchanged the truth of God for a lie, serving the creature rather than the Creator.(Cf Rom. 1, 21, 25) Or some there are who, living and dying in this world without God, are exposed to final despair.
Nothing we’ve read exempts any believer from missionary effort, no matter where they live or what their state of life may be:
Wherefore to promote the glory of God and procure the salvation of all of these, and mindful of the command of the Lord, “Preach the Gospel to every creature”,(Mk. 16, 16) the Church fosters the missions with care and attention.