One of my friends asked me to answer the following question, a question which, although I phrased it somewhat differently, I struggled with myself while getting my first university degree.
"How might we reconcile the belief of Jesus being the only way to reach God with the Revelation 7:9 idea of there being God-followers "from every nation, tribe, people and language"? We certainly know that of the many nations, tribes, peoples, and languages that have existed over the last thousands of years, many have never heard the name of Jesus--or, before that, YHVH. And yet there must be some from these tribes who have followed God, for them to be present before the Throne as white-robed worshippers. How then, in a practical sense, is this possible?
In the Bible there are examples of those who had some sort of relationship with God, though perhaps not knowing fully who He was, such as Balaam, and others such as Abraham who specifically heard His calling outside of the religious establishments of the day. Should we assume that all people groups will have had at least one such person? Or what of the illustration of C.S. Lewis’ Emeth (from The Last Battle), who worshipped Tash by name but Aslan by belief and deed? Could such a thing be possible? It does at least seem to me that there must be some way in which one can be saved by the blood of Jesus, even without perhaps knowing him by name."
There are a number of different possible answers to this question. One fairly typical Protestant answer from Sacred Scripture is that they could be saved by grace through faith just as Abraham was in the Old Testament. In essence, this answer asserts that their faith is what justifies them before God just as it did for Abraham or for us today. This view suggests that the kernel of the Gospel message was already present in the sacred tradition and scripture of the Israelites, which is how they could have faith in Christ and be saved despite not knowing the name of Jesus of Nazareth.
While the Catholic perspective would certainly agree that the Gospel message was often prefigured in the scared tradition and scripture of the Israelites, the explanations are generally different because the Catholic Church does not teach the doctrine of Sola Fide (faith alone).
One fairly typical Catholic explanation from a fellow former Protestant is that the sacrifice of Christ on the cross transcends time, which is why the forgiveness of sins is available before and after Christ's death. This view suggests that it makes sense that for a God who transcends time, when He becomes man and makes the ultimate sacrifice while bearing the weight of our sins, His sacrifice also transcends time. In essence, the God who exists in the fullness of time makes His sacrifice in the fullness of time, pervading all of time with its effects.
The Catholic explanation for all this often invokes the Biblical language of debts, understanding that God forgives our debts to Him when we repent and return to obedience to His commandments. And because the debt has been satisfied for all time by Christ's sacrifice on the cross, the forgiveness of the debt is available for all time for those who repent. This language of debts is not the language I prefer, but it was nonetheless the language used by Christ in the Gospels, both in parable form and in the Our Father, that famous time when Jesus taught his Apostles how to pray.
From both the Protestant and Catholic understandings, it is fairly clear that Abraham could be saved in the Christian sense, whether that sense is Protestant or Catholic. Understanding the circumstances of Abraham can help us to see how God might bring about the salvation of others who have never heard the name of Jesus. Abraham did not know the name of Yahweh or the name of Jesus; both names were revealed after the life of Abraham.
Nonetheless, Abraham did repent and turn toward the Lord in the way that he could do so, having faith in the Lord, a faith which was not diminished because of his limited theological understanding. This makes a great deal of sense, given the general Christian perspective that children who lack theological understanding and may not be able to understand the name of Jesus can still be saved.
Given this, it certainly seems that, at least under certain circumstances, people do not need to have faith in God as named in the Judeo-Christian tradition in order to be saved. Which leads us to the question of whether all people might be saved, the contentious question of universal salvation, but that is a question for another time. For now, it is fairly apparent that for a Christian of either the ancient churches or of the post-Reformation churches, it is the case that people who lived before Christ can be saved, and there is an explanation that fits the evidence of Sacred Scripture.