How were the Old Testament people, for example, Abraham and others saved? Was it through the death of our Lord Jesus Christ; or because of their faith, they "became heir of the righteousness which is according to faith". Also, what is the biblical account concerning their waiting in Hades until our Lord Jesus Christ took them into heaven after His death and descent into Hades.
Salvation can only be through Christ. Although Old Testament prophets died in faith and "became heir of the righteousness which is according to faith", they did not receive salvation until the death of our Lord on the Cross. "These all died in faith, not having received the promises, but having seen them afar off were assured of them, embraced them and confessed that they were strangers and pilgrims on the earth" (Heb 11:13). If Abraham was already saved why would the Holy Scriptures have to tell us "Your father Abraham rejoiced to see My day, and he saw it and was glad" (Jn 8:56) and why would Jacob says, "I have waited for your salvation, O Lord" (Gen 49:18).
In the Holy Book of Ephesians we read "Therefore He says: 'When He ascended on high, He led captivity captive, and gave gifts to men.' (Now this, "He ascended"; what does it mean but that He also first descended into the lower parts of the earth? He who descended is also the One who ascended far above all the heavens, that He might fill all things)" (Eph 4:8-10) or in the Revised Standard Version reads, "When he ascended on high he led a host of captives."
The Fathers interpreted "captivity captive" to mean that as a result of Adam's sin we became captives to the devil who placed us under his authority and the spirits of the departed were caught and brought down to Hades, for Paradise was closed. When Christ gave Himself for us on the Cross He, through His blood, freed the righteous from this captivity to join Him in Paradise (not Heaven), which He opened on that same day.