"As for you, my beloved friend, I loyally believe in your uniqueness; but whenever I try to tell to you wherein it consists, I helplessly describe only a type"

The author is revealing his belief in the individuality and originality of his good friend, but despite his efforts to articulate and describe this distinct nature, he is just able to resort to certain clichéd descriptions that fall short of really catching the essence of his buddy's singularity.