The following are W.G.T. Shedd's comments on WCF 10.3 from his book, Calvinism: Pure & Mixed, in the chapter, "The Doctrine of Decrees" (paragraphing mine):
"... the Confession, in this section, intends to teach that there are
some unevangelized men who are 'regenerated and saved by Christ through
the Spirit' without 'the ministry of the written word,' and who differ
in this respect from evangelized men who are regenerated in connection
with it. There are these two classes of regenerate persons among God's
elect. They are both alike in being born, 'not of blood, nor of the will
of the flesh, nor of the will of man, but of God.' They are both alike
in respect to faith and repentance, because these are the natural and
necessary effects of regeneration. Both alike feel and confess sin; and
both alike hope in the Divine mercy, though the regenerate heathen has
not yet had Christ presented to him.
As this is the extraordinary work of the Holy Spirit, little is said
bearing upon it in Scripture. But something is said. God's promise to
Abraham was, that in him should 'all the families of the earth be
blessed' (Gen. 12:3). St. Paul teaches that 'they are not all Israel
which are of Israel' (Rom.9:6); and that 'they which are of faith, the
same are the children of Abraham' (Gal. 3:7). Our Lord affirms that
'many shall come from the east and west, the north and the south, and
shall sit down with Abraham, and Isaac, and Jacob, in the kingdom of
heaven' (Matt. 8:11).
... That the Church is not to expect and rely upon this
extraordinary work of the Spirit, it is needless to say. That this work
is extensive, and the number of saved unevangelized adults is great,
cannot be affirmed. But that all the adult heathen are lost is not the
teaching of the Bible or of the Westminster Standards" (W.G.T. Shedd, pp. 60-61; underlining mine).
Shedd brazenly DENIES one especially clear text: Romans 10:1-4. So, contrary to Shedd, it IS the teaching of the Bible that those "adult heathen" who are ignorant of Jesus Christ as the end of law for righteousness, are unsaved. It appears quite customary for the Calvinist-Reformed person to make exceptions to the Romans 1:16, 10:1-4, and Mark 16:16 rule; and also to completely obliterate Paul's God-the-Holy-Spirit-breathed argument in Romans 10:13-17, by smashing the links in its logically rhetorical chain.
Shedd on WCF 10.4:
"The declaration in Confession x. 4, and Larger Catechism, 60, does not
refer at all to the heathen as such, but only to a certain class of
persons to be found both in Christendom and heathendom, and probably
more numerously in the former than in the latter. The 'men not
professing the Christian religion' are those who reject it, either in spirit, or formally and actually; that is to say, legalists
of every age and nation, evangelized or unevangelized, who expect
future happiness by following 'the light of nature' and reason, and the
ethical 'religion they do profess,' instead of by confessing sin and
hoping in the Divine mercy.
The Jewish Pharisee, the Roman Julian and Antoninus, the
self-satisfied Buddhist sage following the 'light of Asia,' the
Mohammedan saint despising Christianity, the English Hume and Mill, all
of every race and clime who pride themselves on personal character and
morality, and lack the humility and penitence that welcome the gospel,
are the class spoken of in these declarations.
They press no more, and probably less, upon the heathen than upon
the Christian world; because the most hostile and intense rejection of
the doctrines of grace is to be found in Christian countries, rather
than in Pagan. They do not shut out of the kingdom of heaven any heathen
who has the spirit of the publican, but do shut out every heathen and
every nominal Christian who is destitute of it.
... That this is the correct understanding of the Westminster
Standards is corroborated by the fact that the Calvinism of the time
held that God has his elect among the heathen. The Second Helvetic
Confession (i. 7), teaches it. Zanchius, whose treatise on
Predestination is of the strictest type, asserts it. Witsius and others
suggest that the grace of God in election is wide and far reaching. The
elder Calvinists held with the strictest rigor that no man is saved
outside the circle of election and regeneration, but they did not make
that circle to be the small, narrow, insignificant circumference which
their opponents charge upon them. And there is no reason to believe that
the Westminster Assembly differed from the Calvinism of the time" (W.G.T. Shedd, pp.
61-62; underlining mine).
The pernicious Shedd quotes above came from the chapter, "The Doctrine of Decrees." Similar quotes to those above, come from the chapter, "The Westminster Standards and the 'Larger Hope'":
"In the third place, the Scriptures and the Confession teach that the Divine Spirit exerts his regenerating grace, to some extent, within adult heathendom, making use of conscience, or 'the law written on the heart', as the means of convicting of sin preparatory to imparting the new divine life; and that in the last day a part of God's elect 'shall come from the east and from the west, and from the north and from the south, and shall sit down in the kingdom of God' (Luke 13:29). These are all regenerated in this life. And since regeneration in the instance of the adult immediately produces faith and repentance, a regenerate heathen is both a believer and a penitent. He feels sorrow for sin, and the need of mercy. This felt need of mercy and desire for it is potentially and virtually faith in the Redeemer. For although the Redeemer has not been presented to him historically and personally as the object of faith, yet the Divine Spirit by the new birth has wrought in him the sincere and longing disposition to believe in him. With the penitent and believing man in the Gospel, he says, 'Who is he, Lord, that I might believe on him?' (John 9:36). Such a man is 'regenerated and saved by Christ through the Spirit', and belongs to that class of 'elect persons who are incapable of being outwardly called by the ministry of the word' (Conf. x. 3)." (W.G.T. Shedd, pp. 128-129; italic emphasis Shedd's).