That is a good question and to find the answer you need to consider the beliefs of the older Faiths like Hinduism and Buddhism that do pre-date the birth of Christ. They do not teach that you will go to hell if you do not believe in their version of God like Christianity and Islam do. Their belief has always been that people who sinned a lot in their life and thereby committed harm to other humans or other creatures will "suffer" from their very bad karma tally. That means they will have been reincarnated or reborn into a very unhappy next life. Whereas those who led a very good life will have found the path leading to deliverance from the universal human experience of "suffering", and that through their proper understanding of that condition and by obedience to the right path can human beings break the chain of karma. So before the time of Jesus they would have found deliverance through morality, meditation and wisdom into Mohsha (Hindus) or Nirvana (Buddhists). I personally believe that the Christian belief in "Hell" is really a confused version of the same perception i.e. their next life will not be in some underground furnace ruled by some entity called Satan, but due to their bad karma their rebirth into their next life (either on Earth or on some other planet) will involve very much more suffering (you could describe that as "a life of Hell") just as those born before Jesus with bad karma would have?

This is a question asked from a Christian and biblical context and so is the following answer: The concept presented in the Bible is that the blood of Jesus on the cross flows both ways in time, to those in the future, such as us today, and to those in the past, such as those in the Old Testament. Therefore those who lived before Jesus could also be saved as long as they lived by faith in God's promises of what was to come in Christ. Even their animal sacrifices were an act of faith in the ultimate sacrifice to come in Christ. Or another way of putting it, is the saving blood of Christ is retroactive for people of faith. They didn't live to see Christ come and die on the cross, but they did see it all by faith and God will apply Christ's blood to their faith to bring about their salvation. In a way, we're all the same. We today must live by faith in what happened on the cross in the past, which we did not see ourselves. People before Christ had to live by faith in what would happen on the cross in their future, which they did not see themselves. Either way it's all about faith in what God promised.

The people in the Old Testament times, (from the beginning), did know God, (Yahweh). God was with His people and instructed them to offer a blood sacrifice for their sin. The people confessed and acknowledged their wrongdoing. The animal sacrifices in the Old Testament were symbolic of the eternal blood sacrifice which was to come, (Jesus Christ). In following God's instructions, the blood sacrifices were an act of faith and trust in God. By their faith in God's promises, they were justified in the sight of God.

In the New Testament it reads in Hebrews 10, "For the (Mosaic) law having a shadow of good things to come...For it is not possible that the blood of bulls and of goats should take away sin...we are sanctified through the offering of Jesus Christ once for all."

God counted their faith for righteousness and the blood that Jesus Christ shed was for the sin of all mankind- past, present and future. The people prior to Christ's first advent did indeed confess their sins to God and trusted in the promises that God had given and as a result, they were forgiven.