Diogenesister - The key is vicarious punishment.
Think about the Day of Atonement. The High Priest confessed the nation's sins. The people deserved to die. God accepted the life of an animal in their place. The lamb was sacrificed and the HP presented the blood on the altar in the Holy of Holies. The lamb was punished vicariously in the place of penitent Jews.
Jesus was the ultimate sacrifice. A righteous god must punish sin. We deserve to die for the actual things we do wrong - not for our 'inherited imperfection' as JWs teach. Jesus' suffering and death was the punishment due to us that he took in our place.
Surely he took up our pain and bore our suffering,
yet we considered him punished by God, stricken by him, and afflicted.
But he was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was on him, and by his wounds we are healed.
We all, like sheep, have gone astray, each of us has turned to our own way;
and the Lord has laid on him the iniquity of us all. - Isa 53
He himself bore our sins” in his body on the cross, so that we might die to sins and live for righteousness; “by his wounds you have been healed.” For “you were like sheep going astray,” but now you have returned to the Shepherd and Overseer of your souls - 1 Peter 2
Ask a JW why Jesus died and they will talk about the imperfection that Adam lost and one perfect life being exchanged for another perfect life.
Ask a christian why Jesus died and they will say that he took their punishment on the cross as payment for all the things they do wrong.
This was the thing that Barbour rejected. Russell taught the traditional christian view of Jesus' death as vicarious punishment. Barbour thought this was monstrous and likened it to beating his wife because the children has been naughty. Ever since then the WT claim that it upholds the 'ransom' has been nothing but spin.
Personally I think Barbour was right but I also know that the christian perspective - very much the NT one - is psychologically powerful. The idea that Jesus was on the cross for your sins, not in order to complete some impersonal legal transaction.