This question seems to presume that not everyone has heard, seen and understood enough about God to respond positively to His revelation. Scripture, however, indicates otherwise. In Romans 1:16-2:16 for instance, the apostle Paul declares that the powerful gospel appeal has been sent first to the Jew and then the Gentile (1:16) and the “righteous live by faith” (1:17). This is in contrast with those who continue to “suppress the truth in unrighteousness” (1:18) and as a result will be “given over to their defiled minds” and cut off from further light of God’s gracious truth (1:24-26). (See also Psalm 19)
In other words, those who continually suppress the truth by “trading it in for lies” will grow more and more calloused and cut off from the light of divine revelation. Eventually their consciences will become seared, their hearts hardened, and they may no longer be able to see, hear, understand and turn to God for healing (see also Acts 28:23-28).
On the other hand, if one acknowledges the truth revealed about God through His general light of revelation (nature, conscience, etc), He is faithful to bring them more light. Those who are faithful with a little will be given more (Luke 16:10; also see the story of Cornelius in Acts 10).
Because everyone has a sufficient amount of light to see and believe in Him so as to receive more light, no one has an excuse for unbelief. As Paul explained it:
“For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that people are without excuse.” -Romans 1:20
Those who respond in faith to the general light of God’s common revelation will be entrusted with more light.
“Whoever has will be given more, and they will have an abundance. Whoever does not have, even what they have will be taken from them.” -Matthew 13:12
“He who is faithful in a very little thing is faithful also in much…” -Luke 16:10
“For the grace of God has appeared that offers salvation to all people.” -Titus 2:11
“That was the true Light which gives light to every man coming into the world.” -John 1:9
At this point many ask if I believe general revelation (nature/conscience) is sufficient to save.
No, but neither is special revelation (scripture/gospel proclamation).
Revelation is only sufficient to accomplish what the Bible says it was meant to accomplish. General revelation was sent so that all may acknowledge God as God, whereas special revelation was sent so that all may believe in Christ for eternal life (John 20:31).
The light of revelation is sent so all may see, know and understand truth. It’s mankind’s responsibility to acknowledge and put their trust in that truth, which all people are freely able to do until they have grown calloused and blinded by their own rebellion. Those in rebellion may grow self-hardened and eventually be cut off by God (judicially hardened) in their unbelief (as discussed further HERE).
No one is saved by revelation. We are saved by grace through faith which comes through the revelation of the word (Rom 10:17-18). God is faithful to bring His word to all who acknowledge Him as God through the light they have been given.
* Dr. John MacArthur, in his message covering Romans 2:11-16 (mp3 45-20b), gives a summary of those who did not have the written law and have not heard the gospel:
“Creation, conduct, conscience, contemplation, what they do, how they deal with the good and bad in their own life and how they deal with it in the lives of others indicates that they know the law of God as written in them.
Now, here is the most important thing I’ve said yet. The sum of it is this: If they live up to that much light, and they accept that much light, God will reveal to them the full light of Jesus Christ.
I believe that with all my heart. You see, that’s what it says in Acts 17, “He is not far from us if we would feel after Him.” You see? If they would just take what they have and accept that. John 7:17 – mark it down. “If any man wills to do My Father’s Will, he shall know of the teaching.” If the willing heart is there, he’ll know. ” – John MacArthur
*Answers to common questions and objections are answered in the article HERE.