See the truth about Ed Dingess here and a response to his misguided and poorly thought out reply here. Also see reply to his comment below.
I didn’t read the entirety of this book; much of it is essentially devotional, and much of the rest isn’t disputable: MacArthur does a great job pointing out that the NT describes Christians as slaves of Christ, and does his usual good job of using this type of point as a prod for more earnest discipleship. On that account, Slave is a pretty good piece of work, and MacArthur uses his findings well to debunk the overpersonalized “buddy Jesus” vision of today (though also, he doesn’t go far enough in ridding himself of that, either).
On the other hand, there are two problems here, the first of which has to do with more than the book.
First, I nearly hit the floor when I read pages 1-2. MacArthur correctly notes that many translations obscure this issue by using the word “servant” instead of slave. But he says that he only figured this out in 2007 after reading a book by Murray Harris, and he is wondering why this distinction “escaped me and almost everyone else.” “Had no one uncovered this before Harris in 1999?” he asks.
Um, yes. There are these people called “Biblical scholars” who knew this a long time ago. In fact, MacArthur even quotes Dale Martin’s excellent Slavery as Salvation on a point, and doesn’t remark on the fact that it was written in 1990. So, clearly “someone” had “uncovered this” well before 1999. Not Martin though. Even before that it’s in the scholarship.
Why bring this up? Because it illustrates the problematic disconnect between the Christian academy and the Christian pastorate. In an E-Block article on MacArthur, I had written:
My greatest difficulty with MacArthur, however, has to do with his use of sources. Given his emphasis on excellence in teaching, one might expect him to break from the usual mold of the Popular Pastors and make use of some serious scholarship. This is especially the case given that at TW205 he recommends the use of commentaries and study aids.
However, MacArthur makes almost exclusive use of badly dated commentaries from before the 20th century, or other pastoral authors. The only exception is in HB, where he uses Martin Hengel (though in a chapter that is derived from someone else’s work), and one chapter in FW, where he refers to one scholarly journal article  and a few scholarly commentaries. But this chapter is derived from a response he wrote for the Journal of the Evangelical Theological Society -- why doesn’t he use this type of material for his everyday readers as well?
Slave continues this trend, as MacArthur uses a handful of scholarly sources like Martin’s, but also continues to rely heavily on devotional and pastoral works and even 19th century commentaries. The problem is evident in MacArthur’s statement, “Who could improve on Calvin, Luther, the English Puritans, Edwards, or Spurgeon?” Well, um….Biblical scholars who have a lot more background data on the world of the Bible, that’s who.
Second, and much bigger: MacArthur barely treats the matter of OT slavery, and he needed to check it out a lot more closely. Though he admits the system was “by no means identical” to NT-era slavery, he clearly doesn’t get how “unidentical” they were. OT “slavery” was indentured servitude – and would be the model that would have more strongly informed the Christian faith. In that respect, MacArthur has no inkling of the NT-era concept of patronage that would inform his presentation; although the NT era would have offered little linguistic distinction between the two, conceptually, it is quite different.
Where this is especially a problem is in that NT-era slaves overwhelmingly entered slavery involuntarily – not freely, as we enter into a covenant with God. NT era slaves were prisoners of war, or born into slavery, or came from otherwise oppressed peoples. Because NT-era slavery was mostly involuntary, I predict that certain Calvinist commentators will use Slave to argue for irresistible grace – I can even see seeds of that happening in MacArthur. But that won’t work, because it neglects the patronage aspect of the NT model. In this regard, we might wish that MacArthur would have nuanced his studies with a few other works like Neyrey’s Render to God.
I’d rather you read Neyrey and Martin than read MacArthur. To that end, I recommend Slave only after you’ve read those others. MacArthur has discovered a treasure new to him, but unfortunately, he has taken a valuable pearl and used it in a nose ring.