Once Jesus died, it placed him in a position to bind the strong man (Satan) and take the spoils, including the keys of death and hades. While he need not have the keys to call forth the dead from their graves, the statement sets the stage for the resurrection of the dead. Death and the grave still exist, but the power of opening and closing belonged to Him.
Even now, we must all experience death and the grave. But, since Jesus now has the keys, it is a blessed condition for those who die in the Lord (Rev. 14:13). After His victory over death, He returned to His Father’s house to prepare a place for His bride, and in particular the bridal chamber where He would take her unto Himself. He told the twelve in John fourteen that He was going to the Father to prepare a place for them that where He is, they would be, also. When He returned for her at the end of the age (approximately thirty-seven years later), the threshing floor was purged of the souls who had ever died. This is the first resurrection (Rev. 20) and would consist of a resurrection of life and a resurrection of damnation (John 5:28-29) which John describes as a “thorough cleansing of His threshing floor with a gathering of wheat and a burning up of the chaff “. The gathering in this harvest is a gathering of the righteous dead in the owner’s care and the gathering of the unrighteous dead (Matthew 13:40) who are gathered for burning.
Before Christ’s resurrection, the dead righteous ones were asleep in a place of comfort (Abraham’s bosom, Luke 16). However, they were disembodied spirits longing for expression, much like Demons who would rather abide in pigs than nothing at all. One might describe it as a tranquil existence that Jesus describes as “paradise.” But, it’s not heaven and it’s not like the Garden of Eden that was experienced by Adam. Those who died in the first century were the souls under the altar crying, “How long, O Lord…” They knew the promise of His return was imminent and they were waiting anxiously for vindication and their promised reward. They were among those who experienced the first resurrection and a glorified body that expressed their joy and praise as they joined the heavenly anthem for “they were exalted”. Their rewards are based on what each person had done in the body (Matthew 16:27). When the Son of Man came with His angels in the glory of His Father, he would “repay” each one (cf. Luke 14:44). At that time, Christ would “bring to light the things that were then hidden in darkness and disclose the purposes of the heart. Then each received his commendation from God” (1 Cor. 4:5). Paul, who writes of his own reward, had a “crown of righteousness” laid up for him to be awarded on that day and he adds, “…not to me only but also to all who have loved his appearing” (2 Tim. 4:8). Peter adds that when the chief Shepherd appears, they would receive the unfading crown of glory (1 Peter 5:4). The reason is explained by Paul in the Ephesian letter who teaches that the Christian has obtained an inheritance in him (Ephesians 1:7–11). As pointed out in chapter six, their sealing with the Holy Spirit of promise was the “guarantee of their inheritance until they acquired possession of it” (Ephesians 1:13-14). The possession was at the end of that age and was guarded through faith for a salvation ready to be revealed in the last time” (1 Peter 1:3-5). At the end of the age, when the inheritance was granted, God had united the earthly and heavenly realms of his kingdom. Only, one class reigned with him in glorified bodies who had received their reward.
“Blessed and holy is the one who shares in the first resurrection! Over such the second death has no power, but they will be priests of God and of Christ, and they will reign with him a thousand years.” — Revelation 20:6
They would not go through the fiery trial, again. In the context of Peter’s writing that the “end of all things is at hand,” (1 Peter 4:7), Peter explains,
Beloved, do not be surprised at the fiery trial when it comes upon you to test you, as though something strange were happening to you. But, rejoice insofar as you share Christ’s sufferings, that you may also rejoice and be glad when His glory is revealed.” — 1 Peter 4:12-13
Having already received their reward, these saints who shared in the first resurrection will not experience the second death that would be experienced by “the rest of the dead” who lived not until after the thousand years are finished. You and I will experience it, but the saints who preceded us in judgment will not.
Among those resurrected as having received their reward are the Old Testament worthies, including the martyred prophets, and those beheaded for the testimony of Christ. We acknowledge that not all good on the earth died so they could live with Him. Some did not taste death before Jesus returned. Two classes are referenced as being judged. Paul refers to Jesus Christ “who is to judge the living and the dead and by his appearing and his kingdom (2 Tim. 4:1). We would expect a few from Jerusalem headed Jesus’ warning and fled to the mountains. They did not receive the mark of the beast. John may have been one of the saints who remained till the coming of the Lord as Jesus told Peter about John, “If I will that he tarries till I come, what is that to you” (John 21:22)? Even though they did not die, they would be changed and be caught up together with the resurrected saints.