In the third and fourth centuries in the debates between Augustine and Pelagius over sin and grace, Augustine's position was that God did hold all humanity accountable for the sin of Adam, that original sin. He affirmed that all humanity, all subsequent humanity, inherited from Adam both legal guilt and moral corruption. And this position of Augustine over and against that of Pelagius was affirmed by the church in the Council of Ephesians in the year 431. And that has been the dominant position in the church ever since. But the question then is why? Why would God hold you, and me, and all subsequent humanity both legally guilty and morally corrupt as the result of this original sin of Adam? Augustinians have affirmed in general that that is because of a unique and special closeness that exists between Adam and all humanity.

Now, among Augustinians, there are two primary ways of explaining this closeness. There is a position that's been called realism, which was the position of Augustine himself and many others that accounts for this closeness because of Adam being the first human and the biological head of the human race, and in a very real sense all humans are in Adam, even as an example would be how the author of Hebrews argued that Levi, the founder of the Levitical priests, was in the loins of Abraham when Abraham gave tithes to Melchizedek, who was the forerunner of the order the priesthood that Christ himself would one day have. So, realists would say that this connection is natural.

The other view among Augustinians has been called federal headship, which says that the closeness between Adam and all subsequent humanity is covenantal. They would argue that Adam is the covenant head of a covenant of creation that God had with all humanity. And so, as covenant head, Adam represents us all, and so his actions — in this case his sin — is rightly held we are held accountable for that. In an analogous way, Paul will argue in Romans 5 that Christ is also the covenant head of his people of the covenant of redemption. And so, even as Adam's sin was transmitted to the people of his covenant, so Christ's righteousness is as well.

My own position is that of federal headship. I think this best fits the covenantal structure of Scripture as a whole. It accounts for the comparisons that Paul makes in Romans 5 and also in 1 Corinthians 15 of Christ as the second Adam whose righteousness obedience and righteousness also impacts his people. I think this best accounts for the reason why God holds all humanity accountable for that original sin of Adam.