What was the importance of authentication by a white person on the Narrative of the life of Frederick Douglass?

Not one but
two prominent white abolitionists endorsed Douglass's memoir: William Lloyd Garrison with his
preface and Wendell Phillips through a letter. Both documents offer a legitimizing frame through
which white audiences could read this work. Both men provide a bridge to white audiences by
vouching for Douglass's credibility and character.

This authentication was
crucially important at the time. First, as Garrison points out in his preface, white prejudice
against darker-skinned people was intense, a fact he hopes the memoir will help contest. He
knows he has to step in as a white person, patronizing as it is, to vouch for a black man: White
people (the overwhelming audience for the book, as few African Americans could read) had been
conditioned to treat black people with contempt and suspicion. Therefore, Garrison writes openly
that he considers the memoir to be:

a stunning
blow...inflicted on northern prejudice against a colored complexion.

He also hopes that the memoir will cause white people to
"cease to talk of the natural inferiority" of black people.

That
Garrison has to spend time defending African Americans against claims that they were inferior
shows that, even in liberal abolitionist circles which wanted to free slaves, white people most
often did not consider black people their equals.

Therefore, for Douglass's
book to be taken seriously, both Garrison and Phillips have to state that they have known
Douglass for a long time and attest that he is a good and worthy person. Garrison takes pains to
refer to Douglass's "virtuous traits of character," while Phillips writes to Douglass
(but really to his white readers) that:

Again, we have
known you long, and can put the most entire confidence in your truth, candor, and sincerity.
Every one who has heard you speak has felt, and, I am confident, every one who reads your book
will feel, persuaded that you give them a fair specimen of the whole truth.

Without these prominent men standing behind him, it would be easy
for white people to dismiss this memoir as untrue, biassed, or exaggerated, especially given an
increasingly vocal and strident Southern propaganda machine that at this time was arguing not
only that slavery was a necessary evil but a positive good, spinning tales of slaves that were
well cared for by loving owners on happy plantations. Both Garrison and Phillips go to great
lengths, therefore, to assert that not only is what Douglass saying true but that his experience
is typical and widespread.

Both men use their introductions not only to lend
needed credibility to Douglass himself, but to frame his work as an act of extreme courage in
the face of a grave threat, similar to that which faced the writers of the Declaration of
Independence when they fought tyranny. As Phillips writes:

You...publish your declaration of freedom with danger compassing you around. In all the
broad lands which the Constitution of the United States overshadows, there is no single
spot,however narrow or desolate,where a fugitive slave can plant himself and say, "I am
safe."

Both Garrison and Phillips try to make
Douglass part of a white tradition of struggling for freedom and to use his book to galvanize
the abolitionist movement to work harder to abolish slavery.