Sin Came Through One Man
Sin came into the world through one man, Adam. It is not just that we copy Adam, sinning in the same way, or that we have inherited corruption that gives us a bias towards sin, or that we were all in Adam when he sinned as our ancestor (although these are all true), but that our representative is guilty and we share his guilt. We need another representative. Christ has no sin and gives us all of His righteousness.