If death were not really death and man has an immortal soul, all people are actually immortal. The dead then live on somewhere else and only lay down their earthly life when they die to open their eyes again ‘in the hereafter’.
1 Timothy 6
14 …until the appearing of our Lord, Christ Jesus,
15 (…) the King of kings and Lord of lords,
16 who alone has immortality and dwells in unapproachable light…
Firstfruits
Paul says here that there is only One who has immortality: Christ Jesus. He is the First, and so far the Only One, who has been raised in incorruption. Christ has been raised from the dead, and has death behind Him, death no longer has dominion over Him (Rom.6:9). This is in contrast to other dead in Scripture of whom we read that they were raised, such as Lazarus and the young man of Nain. They received their old life back and later died anyway.
death ineffective
The word that is translated in 1 Tim.6:16 as immortal (athanasia, G110) occurs two more times in 1 Corinthians 15, besides here. In this chapter Paul gives a long explanation of the resurrection and says there that Christ is the Firstfruits of those who are reposing (1 Cor.15:20). He is the First, who has been raised in incorruption, glory, and power (1 Cor.15:42-43). So vivification is: made alive in incorruption (2 Tim. 1:10). Immortality means that death has been put out of action.
Firstfruits and firstfruits
Christ alone has immortality. In 1 Corinthians 15:53-54 the group that will be the next to receive immortality is described. Paul speaks here of a mystery (1 Cor. 15:51). It concerns the ecclesia, the body of Christ. At the parousia the dead in Christ will be raised incorruptible and those who are left alive until that moment will be changed. They will put on immortality as mortal men, receive a new body and be caught up to meet the Lord in the air (1 Cor. 15:51-54; 1 Thess. 4:13-17).
Christ was made alive as the Firstfruits. The word firstfruits refers to the first fruit(s) of the harvest and we often encounter the concept in the Hebrew Bible (e.g. Ex.34:22; Lev.23:10,17 and 20), because the feasts and high days given by God to Israel are related to the harvests.
order
Christ is the Firstfruits and we, as His body, share in that position of firstfruits (Rom.8:23; 2 Thess.2:13) and will be made alive next in order (1 Cor.15:23). But the gathering of the firstfruits always had the purpose and promise that the entire harvest would follow. God is going to destroy death, so that all people will receive immortality!
1 Corinthians 15
20 But now Christ is risen from the dead, the firstfruits of those who have fallen asleep.
(…)
22 For as in Adam all die, even so in Christ all will be made alive. 23 But each in his own order…
Christ is the only one who has immortality, but He is also the guarantee that the rest will follow!