Emphasis added in the quotes below.
Shoghi Effendi, in a letter written on his behalf, singled out The Dawn-Breakers as one of the Baha’i books of “special importance” that “every Baha’i should master and be able to explain.”
In another letter the same year Shoghi Effendi again conveyed: “...The Dawn-Breakers should be mastered by every Bahá’í” and that it should be “read over and over again...
"...appeal entire body American believers to henceforth regard Nabíl’s soul-stirring Narrative as essential adjunct to reconstructed Teaching program, as unchallengeable textbook in their Summer Schools, as source of inspiration in all literary and artistic pursuits, as an invaluable companion in times of leisure... and as unfailing instrument to allay distress and resist attacks of critical, disillusioned humanity."
[Cablegram signed ] SHOGHI 
The term “Dawn-Breakers” was first suggested to Shoghi Effendi in 1931 by George Townshend,  who was later appointed a Hand of the Cause by the beloved Guardian. Regarding the expression “dawn-breakers,” it has since so permeated Baha’i parlance and thought that a simple computer query in the latest version of the Baha’i literature search engine, Ocean 2.0, (available for free for anyone), shows 1,673 results in books and documents! The remaining months of this year 2019, marked by the upcoming Bicentennial of the Birth of the Bab, present us with a special opportunity to honor The Bab and His first followers with focused study, remembrance, and action.
As the Guardian’s secretary wrote on his behalf:
"Shoghi Effendi undertook the translation of “The Dawn-Breakers” only after being convinced that its publication will arouse the friends to greater self-sacrifice and a more determined way of teaching. Otherwise he would not have devoted so much time to it.
Reading about the life and activities of those heroic souls is bound to influence our mode of living and the importance we attach to our services in the Cause. Shoghi Effendi therefore hopes that the friends will read, nay rather study that book, and encourage their young people to do that as well.
The Guardian sincerely hopes and prays that the study of the Dawn-Breakers will inspire the friends to greater activity and more exerted energy in serving the Cause and spreading its message... The life of those heroes of the Faith should teach us what true sacrifice is..."
Again, referring to The Dawn-Breakers specifically:
"Shoghi Effendi would advise the friends... to hold regular study classes and read that book with great care, committing its salient facts to memory, so that while teaching the Cause, they may be able to show the motivating spirit of the Faith by referring to some incidents of those early days.
It is Shoghi Effendi's work in translating Nabil's Narrative that has properly safeguarded the Bab's station in world history!
In a summary statement Shoghi Effendi, referring to the Bab, wrote:
On His early life, His sufferings, the heroism of His disciples, and the circumstances of His tragic martyrdom I need not dwell, as the record of His saintly life is minutely set forth in “The Dawn-Breakers: Nabíl’s Narrative of the Early Days of the Bahá’í Faith”. 
Shoghi Effendi wishes me to acknowledge the receipt of your letter... He is very glad to know that you have liked “The Dawn-Breakers”, for his greatest reward is to see that this work, which has cost him much labour and anxiety, is helping the friends to understand better and more fully the spirit that animates the Movement and the exemplary life of the heroic souls that ushered it into the world.
The Guardian sincerely hopes that by reading this book the friends will be stirred to greater activity and a higher measure of sacrifice, that they will obtain a deeper realization of this Cause whose spread and ultimate victory is entrusted to their care. As some who have read the book have remarked, no one can become familiar with those lives and not be inspired to follow in their way. 
Writing personally to an Assembly the Guardian stated:
In my hours of prayer and meditation in the holy Shrines I will supplicate on behalf of your Assembly, as well as on behalf of the communities you represent, that Divine Guidance may direct your steps, that God’s sustaining grace may aid you to overcome every obstacle, that His strength may be poured out upon you, that His providence and love may enfold you, and that the inspiration of the Dawn-breakers, who proclaimed the birth of His Cause, may carry you to ultimate and total victory. 
As contemporary Baha'i scholar J.A. McLean notes:
Modern approaches to the academic curriculum are normally separative with each discipline being its own specialty. But in The Dawn-Breakers sacred history, drama, heroism, tragedy, devotion, and spirituality are combined in one volume...this exemplary work, now much neglected, can take a broad role in inspiring interdisciplinary studies...literature and art, and all creative movements of the soul, can be inspired... 
The beloved Guardian drained his precious life-force in the final stage of preparing this gift book for the world:
"It took Shoghi Effendi almost two years of research, compilation and translation to complete this remarkable volume."
(Ruhiyyih Khanum, The Priceless Pearl, p. 217)
Hand of the Cause Ruhiyyih Khanum summarized the impact of The Dawn-Breakers and projected its ongoing primacy in the advancement of the Cause of God:
The Bahá'ís of the West emerged from the experience of reading this history of the life and times of the Báb transfigured; it was as if some of the precious blood of those early martyrs had been spattered upon them. They caught a glimpse of the tradition behind them, they saw that this was a Faith for which one carried one's life in one's hand, they understood what Shoghi Effendi was talking about and what he expected from them when he called them the spiritual descendants of the Dawn-Breakers. The seeds this book planted in the hearts of the western followers of Bahá'u'lláh grew and matured in the Ten Year Crusade, and its harvest will continue to be garnered ever more abundantly as the Divine Plan of 'Abdu'l-Bahá goes on unfolding in its conquest of the entire globe.
 21 June 1932
 20 June 1932
 George Townshend, by David Hofman, p.68
 16 April 1933
 1947, 'The World Religion, A Summary of Its Aims, Teachings and History' by Shoghi Effendi
 20 June 1932
 21 June, 1953
 A Celestial Burning, p.29