In short, people are only held accountable for what they know. The Bible says in Romans 1:19-20 that creation alone proclaims that it has a Maker. This is called God’s “general revelation.” Indeed, it is hard to look at the stars or a mountain landscape and not feel a sense of grandeur and realize that you are a very, very small speck. Psalm 19:1-6 says that the stars declare and proclaim God’s work; there is no speech or language where their voice is not heard. In other words, to some degree all creation reveals that there is a God and it has done so in all places, languages, and times in history.
Paul goes on in Romans 2:14-15 to say that when people who do not have God’s Law meet the requirements of that Law, they are showing that in their heart they know that things are supposed to be a certain way and they are trying to meet those requirements. C.S. Lewis calls this “oughtness” in Mere Christianity. This act alone demonstrates a conviction to do “the right thing” even though people fall short.
Although these African tribes may not know the specific requirements of God through head knowledge and even though they may have never heard the name Jesus, the “Law,” or a feeling of how they ought to behave, is written on their hearts. They know the difference between right and wrong. Thus when these hypothetical tribesmen violate their own understanding of what is right, they condemn themselves. Conversely, when they do what they know to be right, their own conscienes defend them. Their clean conscienses save them or their guilty consciences condemn them.
Some people ask this question out of genuine concern, and some ask this question as an excuse to reject God. Again, from Mere Christianity, C.S. Lewis says, “if you are worried about the people outside, the most unreasonable thig you can do is to remain outside yourself.” His statement makes a lot of sense to me. If I were worried about people getting exposed to acid rain, would it make any sense for me to stay outside in the acid rain because others were unable to go inside? Of course not!
To the non-Christian I would just ask one thing. If, as we stated to start this discussion, you’re only held accountable for what you know, then the only question that remains is this: What will you do with the knowledge you have; will you accept or squander the gift that’s been freely offered to you?
To the Christian I say: What’s keeping you from making sure that everyone knows about the freedom that’s been offered to them?