Hodge's treatment of the doctrine of original sin is particularly interesting. It comes out of a debate among American Presbyterians in the 19th century. Some people followed Jonathan Edward's theory of identity (which will the subject of a future post) and the other held to the traditional view of the Westminster Confession, which was strongly influenced by what is referred to as "Federal Theology."
Federal theology is covenant theology. It derives its name from one of the Latin words for covenant (foedus, also pactum). Basically covenant theology works with the Nominalist ontology and therefore assumes that there are no real universals. This creates problems when it comes to the doctrine of original sin, since according to the traditional version of this doctrine the real universal of human nature was damaged and therefore human beings "in Adam" suffer its curse. There is therefore a organic ontological connection between Adam and us. If everyone is, on the other hand, absolutely individual, then mechanism to spread original sin is lost and you've got to come up with something else.
Covenantal theory makes up the difference. The solution is to invent a convoluted theory of different covenants as an organizing theory of salvation history. Regarding original sin, the chief one that defines the divine-human relationship "in Adam" is the covenant of works. God made an agreement with Adam that if he performed the law, then he would live forever. Since Adam didn't do this, then everyone is lost. For this reason, Adam is described by the Federal theologians as being humanity's "Federal representative." Since he was appointed in this role, it makes sense that the atomistic individuals of the human race should have his sin imputed to them. The bottom line is that within this scheme the imputation of Adam's sin is very important because without a universal of human nature to connect people to Adam the reason for the spread of original sin is pretty much inexplicable.
Therefore Hodge is extremely insistent on the idea of the imputation of Adam's sin to his descendants. In contrast to this, the Lutheran scholastics were generally uninterested in the question of whether the passage of original sin actually involved the imputation of Adam's sin or merely the spread of damaged and sinful human nature. Sin is a reality, we have it from conception- good enough, right?
I nonetheless think something else is stake here for Hodge which strikes at the whole way that the Reformed think about theology. One argument that Hodge is at pains to make throughout the section is that Adam's sin being imputed to us is fair. He cites the fact that God states again and again that children will suffer for the sins of their parents. He forgets the statement in Ezekiel saying that will no longer happen. He also tends to forget that if you look at the laws of Leviticus and Deuteronomy, although God does promise to punish for the sins of ancestors, when it comes to the human administration of justice people as a rule do not suffer for the civil crimes of their ancestors or relatives.
Nevertheless, the point is for the Reformed God is fundamentally defined by the law and therefore all of God's actions must be shown to accord with the law. There is grace, but grace always exists for the sake of the law.
Luther had different ideas. In The Bondage of the Will, he acknowledge the mysterious nature of original sin. Human beings are in a sense fated to sin by the sin of Adam. This is inexplicable, since the law (at least when it comes to inter-human relationships) mandates that people suffer only for their own misdeeds. Being subject to original sin, humans are subject to divine wrath. From perspective of our limited minds this makes no sense and doesn't really seem very fair.
What this all suggests is that God is capable of acting in ways that seem to us to be irrational and which are in fact beyond the law. The law cannot account for the mystery of original sin or the depth of divine wrath. This is a fact that should make us despair in our reason and our legal schemes for trying to control God with our works. The law is God's will for us, but he himself is not bound to act in accordance with the law. If he was, he would not be able to send a savior to enter into the law on our behalf. We would need to merit it on our side first before he acted, but that is not what happened.