I consider Dr.Martin's book a most necessary one for the Catholic Church today - one which all serious Catholics, especially those who really love the Church, should read.
In this work, he's done a great service in signalling a clarion call for laity and Church leadership alike to re-assess the impact that the teachings of 20th Century theologians and the Vatican II documents have had upon how Catholics view sin in general, and salvation in particular.
However, despite his magnanimous effort in "Will Many Be Saved?", Dr. Martin utterly fails to address the most fundamental questions regarding sin and salvation:
Namely, what really constitutes Mortal Sin, and how widespread is it in the Church and the world today?
Because Dr. Martin has failed to address those two fundamental questions, I consider his work to be only a moderately valuable and successful one - thus, a ranking of only 3 stars.
Unfortunately, despite Dr. Martin's expose' of the horrifically negative impact upon the Church that the theological teachings Karl Rahner & Hans Urs von Balthasar have had over the past 50+ years, he fails to adequately address in his book the issue of Mortal Sin.
Today, the vast majority of Catholics today - both clergy & laity - believe that "mortal sin is rare anymore" and that "virtually everyone is a good person" and will attain Heaven; essentially, a belief in "quasi-universal" salvation. Even many "good and orthodox" Priests and laity essentially believe and/or teach this today....
Is the reason for that widespread & excessive optimism in the Church about salvation not only because of the impact of Rahner & von Balthasar, but also because the Church has itself allowed the faithful to believe in a definition of Mortal Sin which is itself different and more lax compared to that taught before Vatican II?
I believe so.
Compare the definition of Mortal Sin which the Church has "officially" proclaimed since Vatican II (see paragraphs 1857-1861 in the new Catechism) to what was taught prior to Vatican II.
Now, in supposedly "official" Church teaching, committing a Mortal Sin requires that a grave sin is committed with "full knowledge", and that there aren't any mitigating factors that would diminish the freedom and culpability of the person (however, that definition forgets that serious and habitual sin, in and of itself, progressively "darkens the mind, hardens the heart, and weakens the will").
Prior to Vatican II, all that was required for a Mortal Sin to be committed was that "serious reflection" must have taken place (per the Baltimore catechism) with regard to the gravity of the serious sin.
St. Thomas Aquinas famously taught the following ([...] ):
"... sometimes an erroneous conscience does not absolve or excuse from sin, namely when the error itself is a sin, proceeding from ignorance of that which someone is able to and obliged to know, as for example, if someone believed fornication to be simply a venial sin, and then, [if he committed fornication], although he would believe that he was sinning venially, he would not be sinning venially, but mortally" (Quodlibetal 8, q. 6, a. 5).
Basically, St. Thomas is teaching that if we've previously had the opportunity to understand what is gravely sinful, but have been derelict in the duty to do so, we can no longer be considered as non-culpable for committing a Mortal Sin.
Contrary to what St. Paul himself infallibly taught in 1 Cor. 6:9, many Christians today no longer believe as the Catholic Church taught before Vatican II that Adultery, Homosexual acts, nor Fornication are inherently Mortal Sins - in large measure because of misconstrued non-culpable ignorance (i.e. mistakenly thinking that without "full knowledge", a Mortal Sin hasn't occurred).
Hopefully, Dr. Martin, or other prominent and knowledgeable Catholic theologians/teachers (hopefully, our next Holy Father after Benedict XVI!), will correct how the Catholic faith truly teaches on the matter of Mortal Sin. Only that corrected teaching will allow for us to get out of the morass of rampant Mortal Sin so widespread within the Church today, as well as in much of western culture.
With his work "Will Many Be Saved?", Dr. Martin merely introduces that the Church is in a crisis. But, he fails to propose HOW we can get out of it.
A concerted focus upon a corrected and accurate teaching about Mortal Sin MUST take place in the Catholic Church for that corrective action to happen....