Perhaps the biggest is his claim that, 'Justification theory posits a God of strict justice who holds all people accountable to a standard they are intrinsically unable to attain, and this seems unjust' (45 - emphasis original). I think this is a question worth asking. How can God be just for holding people accountable for failing to do the impossible, be perfect? As Campbell points out, yes the gospel does provide a way out, but that provision does not make the initial scenario any more just. Some (a small group) will simply escape its unfairness. The majority have to endure a fundamentally unjust system and are held accountable for sins they can't help but commit (48). And, the punishment is severe (especially if one is not an annihilationist).
A second point is that 'Justification theory does not explain why Christ must atone as against other people or things, and especially, in place of the established temple cultus' (49). He deals specifically with Anselm's argument that so much sin needed to be atoned for that an offering of unlimited value was required. Only the death of God could would be sufficient compensation (50). Campbell notes that there is a fundamental mistake in this line of thinking that in the end forces us into a ridiculous view of God were it to be true. Specifically, justification theory fails to notice the distinction between value and price (53). Clearly Christ's death is valuable, but this theory seems to cast that value into economic terms. Yes, it does make sense in some cases to have an economic price for a crime, but certainly not in every case. A murder who is put to death did not pay for his crime in his death. Being executed gives payment to no one. Thus to view Christ's death as atoning by paying a price then,' the underlying premise would have to be granted that all human action is essentially economic...' (52). Even more damning,
Moreover, it simply seems ludicrous to imagine that human wrongdoing is essentially economic in any sense with respect to God - that human sins are a violation of God's rights to certain goods and services. God is both transcendent and Creator! Nothing a person can do could deprive God of something, and certainly not of anything material...The only thing God can be deprived of is the honor and respect due him and his decrees. Hence, the economic view of wrongdoing makes little sense in relation to the God posited by the theory of Justification (52).
The Bible does use the language of payment (e.g., ransom) in relation to Christ's death, so there's no need to abandon economic language. We just need to recognize that it's metaphorical (54). Other grounds must be sought for why Christ had to die to atone, as the Bible says he did.
The third issue, which I found to be the most interesting was that, 'Justification theory harbors a cluster of complex problems with respect to faith, in two main variations. The "Arminian" variant struggles to explain faith fully, and, in particular, how individuals can actually exercise faith in order to be saved. The "Calvinist" variant can get beyond these difficulties by introducing revelation and election at the point of faithbut then runs into further problems in relation to the privileging of faith and its gifting to individuals who have negotiated phase one. Ultimately, both variants collapse (55).
Integral to justification theory is faith. One must believe to be saved. You become a Christian by choosing to believe (if you're an Arminian, at least). The problem is that you can't choose to believe. Beliefs aren't chosen. No act of will can make you believe something you aren't convinced of. So it boils down to being convinced? Unfortunately, you are being asked to believe unverifiable claims like, 'Jesus died for your sins.' There is no way that anyone could figure it out on their own. Only God knows that and it can only become known to us if God chooses to disclose it to us (58). So we end up with an epistemological problem. We are guilty and should know that we are guilty apart from any special revelation from God. This information is readily available to us by nature. However, the way out of the predicament isn't similarly attainable without tapping into an alternative way of knowing, namely revelation (55). Thus the criteria of salvation is divorced from the criteria of judgment. Calvinists attempt to get around this by attributing salvation solely to God, but that then eliminates the need to have any saving criteria, including faith. Why is faith important? Why not love? The Calvinist model cannot explain this, yet Paul does 'massively privilege faith' (59). And from this conundrum, I see no way out.
As the book progresses we will get to see how his theory avoids the shortcomings of justification theory, but even if his presentation doesn't hold up under scrutiny, his exposition of the weaknesses of justification theory are invaluable.