I am going to be exploring the issue of "implicit faith" and why such a concept can be self-contradictory and absurd. Before doing that, however, I would like to acquaint the reader with a sample of the many statements which the Church has made on the need for explicit faith in the Blessed Trinity and Incarnation:
Pope Benedict XIV, Cum Religiosi (On Catechesis), 1754, #1, 4: "We could not rejoice, however, when it was subsequently reported to Us that in the course of religious instruction preparatory to Confession and Holy Communion, it was very often found that these people were ignorant of the mysteries of the faith, even of those matters which must be known by necessity of means; consequently, they were ineligible to partake of the Sacraments. [...] school-masters and mistresses should teach Christian doctrine; that confessors should perform this part of their duty whenever anyone stands at their tribunal who does not know what he must by necessity of means know to be saved."
"All ceremonies are professions of faith, in which the interior worship of God consists. Now man can make profession of his inward faith, by deeds as well as by words: and in either profession, if he make a false declaration, he sins mortally." (Summa Theologica, Ia IIae, q.103, a.4)
"The custom of the Church has very great authority and ought to be jealously observed in all things, since the very doctrine of catholic doctors derives its authority from the Church. Hence we ought to abide by the authority of the Church rather than by that of an Augustine or a Jerome or of any doctor whatever. Now it was never the custom of the Church to baptize the children of the Jews against the will of their parents, although at times past there have been many very powerful catholic princes like Constantine and Theodosius, with whom most holy bishops have been on most friendly terms, as Sylvester with Constantine, and Ambrose with Theodosius, who would certainly not have failed to obtain this favor from them if it had been at all reasonable. It seems therefore hazardous to repeat this assertion, that the children of Jews should be baptized against their parents’ wishes, in contradiction to the Church’s custom observed hitherto. There are two reasons for this custom. One is on account of the danger to the faith. For children baptized before coming to the use of reason, afterwards when they come to perfect age, might easily be persuaded by their parents to renounce what they had unknowingly embraced; and this would be detrimental to the faith. The other reason is that it is against natural justice..." (Summa Theologica, IIa IIae, q.10, a.12)
"If we consider unbelief as we find it in those who have heard nothing about the faith, it bears the character of punishment, not of sin, because such ignorance is the result of the sin of our first parents. When such unbelievers are damned, it is on account of other sins, which cannot be taken away without faith, not because of their sin of unbelief." (Summa Theologica, IIa IIae, q.10, a.1)
"Everyone is bound to believe something explicitly...even if someone is brought up in the forest or among wild beasts. For it pertains to Divine Providence to furnish everyone with what is necessary for salvation, provided that on his part there is no hindrance. Thus, if someone so brought up followed the direction of natural reason in seeking good and avoiding evil, we must most certainly hold that God would either reveal to him through internal inspiration what had to be believed, or he would send some preacher of the faith to him as He sent Peter to Cornelius (Acts 10:20)." (The Disputed Questions on Truth, q.14, a.11)
"After grace had been revealed, both learned and simple folk are bound to explicit faith in the mysteries of Christ, chiefly as regards those which are observed throughout the Church, and publicly proclaimed, such as the articles which refer to the Incarnation, of which we have spoken above (Question 1, Article 8). As to other minute points in reference to the articles of the Incarnation, men have been bound to believe them more or less explicitly according to each one's state and office." (Summa Theologica, IIa IIae, q.2, a.7)
"It is impossible to believe explicitly in the mystery of Christ, without faith in the Trinity, since the mystery of Christ includes that the Son of God took flesh; that He renewed the world through the grace of the Holy Ghost; and again, that He was conceived by the Holy Ghost. Wherefore just as, before Christ, the mystery of Christ was believed explicitly by the learned, but implicitly and under a veil, so to speak, by the simple, so too was it with the mystery of the Trinity. And consequently, when once grace had been revealed, all were bound to explicit faith in the mystery of the Trinity: and all who are born again in Christ, have this bestowed on them by the invocation of the Trinity, according to Matthew 28:19: 'Going therefore teach ye all nations, baptizing them in the name of the Father, and of the Son and of the Holy Ghost.'" (Summa Theologica, IIa IIae, q.2, a.8)
"Explicit faith in those two things was necessary at all times and for all people: but it was not sufficient at all times and for all people." (Summa Theologica, IIa IIae, q.2, a.8)
"If a man born among barbarian nations, does what he can, God Himself will show him what is necessary for salvation, either by inspiration or sending a teacher to him." (St. Thomas Aquinas, Sent. II, 28, q.1, a.4, ad 4)
"If a man should have no one to instruct him, God will show him, unless he culpably wishes to remain where he is." (St. Thomas Aquinas, Sent. III, 25, q.2, a.2, solute. 2)
The Athanasian Creed, infallibly declared at the Council of Florence and reaffirmed again at the Council of Trent:
1. Whosoever will be saved, before all things it is necessary that he hold the catholic faith;
2. Which faith except every one do keep whole and undefiled, without doubt he shall perish everlastingly.
3. And the catholic faith is this: That we worship one God in Trinity, and Trinity in Unity;
28. He therefore that will be saved must thus think of the Trinity.
29. Furthermore it is necessary to everlasting salvation that he also believe rightly the incarnation of our Lord Jesus Christ.
30. For the right faith is that we believe and confess that our Lord Jesus Christ, the Son of God, is God and man.
44. This is the catholic faith, which except a man believe faithfully he cannot be saved.
Pope Paul III, Council of Trent, Session. 6, Chapter. 3, ex cathedra: "But although Christ died for all, yet not all receive the benefit of His death, but those only to whom the merit of His Passion is communicated."
In 1703 during the reign of Pope Clement XI when the missionary effort to the Amerindians was at its height, the Holy Office responded to an inquiry from the Bishop of Quebec: "Question. Whether it is possible for a crude and uneducated adult, as it might be with a barbarian, to be baptized, if there were given to him only an understanding of God and some of His attributes, especially His justice in rewarding and punishing according to this remark of the Apostle: 'He that cometh to God must believe that He is and that He is a rewarder' (Heb. 11:16), from which it is to be inferred that a barbarian adult in a certain case of urgent necessity, can be baptized even though he does not explicitly believe in Jesus Christ. Response. 'A missionary should not baptize one who does not explicitly believe in the Lord Jesus Christ, but is bound to instruct him about all those matters which are necessary, by a necessity of means, in accordance with the capacity of the one to be baptized.'" (Denzinger, 2380)
To an additional query the Holy Office responded, "that even an adult Indian at the point of death, must make an act of faith in the Trinity and the Incarnation before he could be baptized." (Denzinger, 2381)
"Still we answer the Semipelagians, and say, that infidels who arrive at the use of reason, and are not converted to the Faith, cannot be excused, because though they do not receive sufficient proximate grace, still they are not deprived of remote grace, as a means of becoming converted. But what is this remote grace? St. Thomas explains it, when he says, that if anyone was brought up in the wilds, or even among brute beasts, and if he followed the law of natural reason, to desire what is good, and to avoid what is wicked, we should certainly believe either that God, by an internal inspiration, would reveal to him what he should believe, or would send someone to preach the Faith to him, as he sent Peter to Cornelius. Thus, then, according to the Angelic Doctor [St. Thomas], God, at least remotely, gives to infidels, who have the use of reason, sufficient grace to obtain salvation, and this grace consists in a certain instruction of the mind, and in a movement of the will, to observe the natural law; and if the infidel cooperates with this movement, observing the precepts of the law of nature, and abstaining from grievous sins, he will certainly receive, through the merits of Jesus Christ, the grace proximately sufficient to embrace the Faith, and save his soul." (St. Alphonsus, The History of Heresies, Refutation 6, #11, p. 457)
"We also learn from Christ and his Church, that the explicit faith in the mysteries of the Holy Trinity and of the Incarnation of the Son of God is also required as a necessary means of salvation." (Father Muller, The Catholic Dogma, page 10)
The Sacred Congregation of the Propagation of the Faith, under Blessed Pius X, in 1907, in answer to a question as to whether Confucius could have been saved, wrote:
"It is not allowed to affirm that Confucius was saved. Christians, when interrogated, must answer that those who die as infidels are damned."
Hebrews 11:6 -- "But without faith it is impossible to please God. For he that cometh to God, must believe that he is, and is a rewarder to them that seek him."
Annotation of the 1582 Rheims New Testament
6. He that cometh. Faith is the foundation and ground of all other virtues and worship of God, without which no man can please God. Therefore if one be a Jew, a heathen, or an heretic, that is to say, he be without the Catholic faith, all his works shall profit him no whit to salvation.
"If, according to the word of truth, no one is delivered from the condemnation which was incurred through Adam except through faith in Jesus Christ, and yet from this condemnation they shall not deliver themselves who shall be able to say that they have not heard the gospel of Christ, on the ground that 'faith cometh by hearing,' how much less shall they deliver themselves who shall say, 'We have not received perseverance!' For the excuse of those who say, 'We have not received hearing,' seems more equitable than that of those who say, 'We have not received perseverance;' since it may be said, O man, in that which thou hadst heard and kept, in that thou mightest persevere if thou wouldest; but in no wise can it be said, That which thou hadst not heard thou mightest believe if thou wouldest. And, consequently, both those who have not heard the gospel, and those who, having heard it and been changed by it for the better, have not received perseverance, and those who, having heard the gospel, have refused to come to Christ, that is, to believe on Him - since He Himself says, 'No man cometh unto me, except it were given him of my Father,' - and those who by their tender age were unable to believe, but might be absolved from original sin by the sole laver of regeneration, and yet have not received this laver, and have perished in death: are not made to differ from that lump which it is plain is condemned, as all go from one into condemnation. Some are made to differ, however, not by their own merits, but by the grace of the Mediator; that is to say, they are justified freely in the blood of the second Adam." (Saint Augustine, On Correction and Grace, 11-12)
Haydock Commentary on Romans 3:20 et seq.
Now, at the coming of Christ, the justice of God, that is, the justice by which he made others just, and justified them, cannot be had without faith in Christ, and by the grace of our Redeemer Jesus Christ, whom God hath proposed to all, both Gentiles and Jews, as a sacrifice of propitiation for the sins of all mankind, by faith in his blood; that is, by believing in him, who shed his blood and died for us on the cross.
Matthew 27: 52-53 -- When explicit faith in Christ became necessary for all.
"And the graves were opened: and many bodies of the saints that had slept arose, And coming out of the tombs after his resurrection, came into the holy city, and appeared to many."