Humans were as originally created sinless. We still retain the image of God in our ability to reason, and make choices based upon that reason. God is perfect justice, perfect mercy. When humanity rebelled, justice required the penalty assured before the rebellion, death. However, in mercy, God provided a system of atonement (remember the sacrifices of Cain and Abel ?) Blood was spilled from the beginning, pointing forward to Christs final sacrifice,. With the Jews the sacrificial system was refined and specific laws were given, but none were the perfect sacrifice, They were temporary and had to be repeated, but they all pointed forward. This system and it's laws were eliminated when Christ (Paul called him the second Adam) a sinless human (as Adam was originally) lived a perfect life, which was required, and died the death required for all humans, the perfect sacrifice, and these were imputed to those that believe. God is perfectly just, Christ's death met the standard of punishment. Christ's life meets the standard of perfection for us, perfectly merciful. One can benefit from this by choosing to do so, God would never compromise your free will, your right to choose, by compelling you to live when you choose to die ( the ultimate, final death, oblivion ). As to the souls before the crucifixion, they were participating in a symbolic pre acceptance of the results of the Crucifixion, which was adequate. As to the millions who have never known about God through history, he is perfectly just and perfectly merciful, and how he deals with them I can only surmise it will be just and merciful.
