I'm not really sure it's the best place to start a discussion about the book, but the two prefaces seem to keep nagging at me, particularly one phrase - mental assent.
On page ix, (Packer's preface), I read:
God has joined faith and repentance as the two facets of response to the Savior and make it clear that turning to Christ means turning from sin and letting ungodliness go (paragraph 1, sentence 3)
Simple assent to the gospel, divorced from a transforming commitment to the living Christ, is by biblical standards less than faith, and less that saving, and to elicit only assent of this kind would be to secure only false converts (par 2, sen 6)
So what is in question is the nature of faith (par 1, sen 8) - I would agree with this statement, by the way. This should be a question as to the nature of faith.
Then on page xi (Boice's preface), I read:
Did I say weakness? It is more. It is a tragic error. It is the idea - where did it come from? - that one can be a Christian without being a follower of the Lord Jesus Christ. It reduces the gospel to the mere fact of Christ's having died for sinners, requires only of sinners that they acknowledge this by the barest intellectual assent, and then assures them of their eternal security when they may very well not be born again. (par 4, sen 1-2)
What I see in both of these prefaces is that both of these men equate faith with mental assent to some facts, or "the barest intellectual assent"
Here is Packer again:
"faith and repentance as the two facets of response"
Then he goes on to define (or describe) what these two facets are:
"Simple assent to the gospel, transforming commitment"
And now Boice again:
"It reduces the gospel to the mere fact of Christ's having died for sinners, requires only of sinners that they acknowledge this by the barest intellectual assent"
Neither of these men define or describe faith as full assurance, personal conviction, trust, expectant hope.
By their insistence that a removal of commitment leaves only a "simple assent" or "barest assent", they are, in essence, saying that faith = intellectual assent.
So they have posited a view that assent to facts is not enough, but that this assent to facts must be coupled with a commitment to follow. We can therefore conclude that their idea of "saving faith" would be the following two components:
facts + following