It seems that the main answer to this question is that Christ had to descend to Hell to preach to the spirits there to then allow those people to come into heaven.
I have never found this answer satisfactory. It has several problems with it. The most obvious problem is that Moses and Elijah were in heaven before Jesus died. (This is clear because of the transfiguration.) It is probably safe to assume that Abraham was in heaven because of the parable of Lazarus going to Abraham’s bosom. (granted it is simply a parable) And of course Elijah was carried to heaven in a fiery chariot. This is all predating Christ.
The response will probably be that time for God is not linear. I think that that introduces a different problem. We are made to be limited in time and space. God created us to have these limitations. He intended that there would be eskimos and aborigines who never heard of the name of Jesus. This is part of His plan and is not a frustration to Him. He demanded that we fill the earth and multiply. I’ve always wondered why. Wouldn’t it be better to have everyone gathered around at one time and then die and rise so everyone can know about it? The fact that he didn’t tells me that God intends on using space and time as a part of His plan. He intends that some people have very little information to work with. I believe it is His mercy, but i don’t know for sure. Some may be saved even if by the skin of their teeth, and some may fully embrace even the hardness of God and take Him in fully, as in the Eucharist.
I honestly believe that the answer to this question is that those people prior to Christ and away from any means of hearing were saved exactly as we are. Through faith in Christ. [We shouldn’t forget that the old testament is full of names for Jesus! (i.e. the anointed one, the root of Jesse, the morning star)]
This is what Paul is saying in Romans 4:3 "What does the Scripture say? ‘Abraham believed God, and it was credited to him as righteousness.’
(BTW. I don’t intend this to be an argument for sola fides.)
Romans 10:13,17-18.
"12 For there is no difference between Jew and Gentile–the same Lord is Lord of all and richly blesses all who call on him, 13 for, “Everyone who calls on the name of the Lord will be saved.” …17 Consequently, faith comes from hearing the message, and the message is heard through the word of Christ. 18 But I ask: Did they not hear? Of course they did: “Their voice has gone out into all the earth, their words to the ends of the world.”.
Paul is quoting Psalms 19 concerning creation. As he phrases it in the first chapter of Romans, Creation testifies even concerning His Godhead, so that all men are without excuse. The simplest explanation (and therefore the most likely) is that we all have some opportunity to choose Christ or anti-Christ. Whether we have heard the good news or not we all understand this choice. Anything beyond this is ‘multiplying entities beyond necessity.’
-Justin