The Reformed notion of Federal Headship states that all of mankind lives under the representative umbrella of a father figure, namely Adam or Jesus. They say the reason why God can consider all men subject to the consequences of Adam’s deliberate sin, even though we didn’t personally sin, is because God judges us ‘in Adam’. Likewise, when a person is saved, the Reformed say that person is worthy of the blessings of salvation, not for anything they did, but because of the perfect obedience of Christ, with God judging them to be ‘in Christ’. To put it crudely, it’s as if all mankind were placed in one of two boxes, one labeled “Adam”, the other labeled “Jesus”. God doesn’t judge you personally, only by proxy, only based upon the box you’re in.
With that imagery in mind, popularly termed “Imputation,” it can be easily seen why Protestants believe salvation cannot be lost and why they shudder to hear Catholics teaching that our works play a role in our salvation: If we are ‘covered up’ (hidden) in the box labeled “Jesus,” and that’s all God judges us worthy of heaven or hell based upon, then obviously God wont be judging us based on our personal sins (causing us to deserve hell) or on our person good works (causing us to deserve heaven). This is what Protestants mean by “Christ Alone” and “Grace Alone”.
But if this Federalism/Imputation framework is true, then why does the Bible frequently speak of our personal sins being forgiven and our personal sins being the basis of our damnation? Why is God concerned about our personal failings if He is judging us solely based on the failings of Adam? If we are in the box labeled “Adam,” and that’s all God looks at, why does God care or judge us according to the box of our own sins? The only answer I can envision is that Federalism/Imputation must wrong (or only half-true). It is wholly inconsistent and even equivocal for a Protestant to say Jesus as Federal Head represents the believer entirely but Adam as Federal Head represents us only partially. Just as “Jesus plus our works” is anathema to Protestant ears, by the same logic, so must “Adam plus our works” must be rejected…and yet the latter is contrary to Scripture’s frequent claims of our personal sins being the object of God’s wrath and forgiveness (Romans 1-3).
This is not to say that Adam and Jesus are not ‘heads of humanity’ in a real and crucial sense, because Catholicism certainly believes they are heads. The point is that it cannot be Sola Headship as the Reformed teach, but rather (somehow) a combination of headship and our personal living.