The Biblical doctrine of Imputation and Impartation
The Scriptures teach us that death was introduced into the creation by Adam as a result of his sin (Rom.5:12-20) and God with regard to sin and condemnation has used this to condemn the entire human race by association [Adam's guilt is imputed to our 'moral accounts' and his fallen and rebellious nature is imparted to each and every one of us (though, on judgement day, we will only be held accountable for our own specific sin, not Adam's as well.)]. Just as in competition the individual competitor or team either attain victories (or suffer losses) on behalf of the community that they represent (be it either a school, a village, a town, a county, a state, a country or the entire human race) so in this case, Adam, as our representative, suffered the loss of being in that righteous relationship with God, because of his sin, the consequences of which, in turn, have been passed on to us.
This might, at first sight, seem incredibly cruel and unfair of God to do this but his reason for doing this is so that he can use exactly the same principle with regard to salvation in respect of Christ [In order for God to use the principle with respect to redemptive salvation he has also to use exactly the same principle with respect to moral guilt ('sin') and condemnation, otherwise God is violating his just nature and God cannot do that]. This means that salvation can actually be attained solely by Christ, but its benefits can be credited/imparted to us as the community (in this case 'the human race') that Christ represents.
If God did not use this principle then each one of us would individually, have to attain salvation for ourselves, which, for a sinner to try and do in the face of an absolutely holy and righteous God is absolutely impossible (and even that is the biggest understatement ever in the entire history of the human race!)
In other words, God has to condemn the entire human race ['in Adam'] in order that he might then be able to redeem them ['in Christ'] (Rom.11:32). This is what Paul is talking about in his letter to the Romans (Rom.5:12-20) and his first letter to the Corinthians (1Cor.15:20-23).
God could not leave the entire human race in a state of perpetual 'innocence' since it was necessary for us to 'grow up' morally speaking so that we would truly be 'in the image of God' in the fullest and most mature sense. For this reason humanity has to go through the experience of sin and all it's consequences (this is what human history is really all about - the whole of human history has a salvific [salvific = relating to salvation] dimension to it) in order to then experience the saving grace of God which is the means by which we attain spiritual maturity and take our place along side God as 'heirs with God and joint heirs with Christ' (Rom.8:17). How would we ever know of God's grace, mercy redemption etc. unless we had first experienced sin?
Does this answer your question?
Simonline.