Is implicit knowledge of Christ saving? Specifically, is it necessary to have explicit knowledge of Christ or is it enough to have faith in God (belief in one leads to the other)? If explicit knowledge is necessary for salvation, what is the soteriological effect of being unable to adequately describe the nature of the Trinity without falling into a heresy of either modalism or subordinationism? Is C.S. Lewis correct in asserting that “there are people in other religions who are being led by God’s secret influence to concentrate on those parts of their religion which are in agreement with Christianity, and who thus belong to Christ without knowing it?” What is the role of prevenient grace in non-Christians, given that a recent study suggested that three billion in the world have not heard the Gospel? Was Karl Barth correct in writing: “Where Christians are unwilling to love men, how can they say that God loves them or that they are loved by God? They can only prove thereby that they are not too sure about this themselves, and perhaps that they are not even aware of it. For they themselves are only man, and they are always non-Christians as such. As the friends of God they are also His enemies, as believers godless. If they are aware and sure of the fact that God has loved them as such, they must also be aware and sure of this fact in respect of others too. The decisive presupposition in respect of every man can be only that Jesus Christ has died for his sin too, and for his salvation. They must regard and approach every man from this angle. Hence they can never be against men?”
I assume that by “implicit knowledge” you mean that a person obeys God because of their conscience or some sense of right and wrong, thus showing that they have a kind of “faith” in God even though they do not have consciously “correct” belief in the gospel. I see very little support for this idea in the Bible. The only scripture in the New Testament which can be seen to point in this direction is Romans 2:12-16 in which Paul says that those who, by nature, do the things required by the law can be justified by doing so. The problem is that, in the context, he is saying this to shame the Jews who thought they deserved salvation because of their righteous lives, despite the fact that they were sinners. This passage is not teaching salvation by implicit knowledge but rather is shaming the Jews who, despite explicit knowledge, still do not obey God. This is the only passage in the New Testament which even suggests the possibility that implicit knowledge is valuable and I believe it is not promising salvation on this basis.
The tenor of the New Testament teaching about salvation focuses on explicit knowledge. We are told to repent and be baptized in order to be saved. How can one implicitly repent and be baptized? We are told that if we call on the name of the Lord and put our faith in him we will be saved. Again, it is hard to even conceive of an implicit version of this activity. To support the idea of “implicit knowledge” leading to salvation seems to equate to works salvation, as if obeying our conscience or being sincere can somehow make us righteous enough to be saved without faith in the blood of Jesus. To claim that Paul is supporting this conclusion in Romans 2:12-16 flies in the face of the message of the book, which is that salvation is by faith in Jesus, not by works.
About modalism or subordinationism, these are incorrect theologies. It is hard to determine how far one’s understanding of exactly who Jesus is can diverge from the correct biblical teaching without forfeiting our salvation. There are many unsophisticated believers who probably could not even understand the difference between modalism or docetism or monothelitism, never mind decide which is a right or wrong description of Jesus. I will avoid speculating on how far our explicit knowledge of the nature of God and the “trinity” can vary from the correct understanding, but I believe that God will hold us accountable for what he has given us sufficient ability to understand. Personally, I doubt that a person will go to hell simply because their understanding of Jesus approaches something like modalism. If someone calls himself a teacher, that would be different. James taught that those who teach are held to a higher standard (James 3:1-2). It is one thing to be a bit confused about the nature of Christ and the Godhead and it is another to teach publicly that Jesus is not God or that he only appeared to live in a physical body.
It is not my place to judge, but I believe that C.S. Lewis goes too far toward universalism in his statement. I will let God judge and have no desire whatsoever to take his prerogative in this decision, but my understanding of the scriptures is that “there is no other name under heaven by which we must be saved.” and “No one comes to the father but through me.” and “Those who call on the name of the Lord will be saved.” as well as “those who believe and are baptized will be saved.” All of these point strongly toward explicit obedience. There are dozens of passages which seem to narrow down who is saved. We are saved by putting our faith in Jesus Christ. If God chooses to save those who only implicitly believe, I will be happy about that, but I choose to be “safe.” I definitely disagree with CS Lewis’ statement. Hindus do not receive the gift of the Holy Spirit unless they are baptized into Christ (thereby explicitly rejecting Hinduism). If we accept Muhammed, then we believe that Jesus was not crucified, that he is not God and that he is not Savior. If God chooses to forgive such a person, that is fine with me, but I see absolutely no reason in the scripture to trust to this possibility.
About prevenient grace, that term is not found in the Bible and it is questionable that it is in the Bible, depending on how it is defined. If prevenient grace is defined as God foreknowing those who will believe in Jesus and put their faith in him, then it seems to not be all that closely related to the other questions you are asking. Almost by definition, prevenient grace applies to those who become Christians.
About those who have not heard of Jesus, as above, I will leave the decision about those people in God’s hands. The number you heard quoted is quite exaggerated. I have been all over the world and I have literally not yet met a single person who had not heard of Jesus and were not aware of the general idea of what Christianity is about. I have seen various figures for those who have not heard about the gospel. Between a half a billion and a billion is a better number than the clearly exaggerated number three billion. However, the size of the number is really not relevant to what the Bible teaches. It is tempting to be sentimental about those who have not heard about Jesus–to wish them into heaven. A better idea is to take definite steps to bring the message about Jesus to more people so that more people can be saved. Surely their best hope is to put their faith in Jesus. Speaking for myself, I would not want to come before God on Judgment Day, hoping to enter heaven based on my righteous life.
I do not have a particular response to Barth’s statement except to say that I agree that the most effective way we can bring the gospel to those who do not know God is to show the love of God to those people. Truly, we are ambassadors for Christ and, in the context of 2 Corinthians 5:20, Christ’s ambassadors respond to and show God’s love to others.