I would say that one of the reasons why Nabokov's work is so important rests in its title. As time passes in our lives and we wish to give voice to our identities in the past, we call to the heavens and to ourselves: "Speak, memory." The call of "Speak, Memory" is a desire to use our memory to recapture times that have passed. They will no longer be experienced, so there is a desire to reclaim them. The problem is that our memory of those events changes as time passes. Nabokov himself speaks to this: "The following of such thematic designs through one's life should be, I think, the true purpose of autobiography."
It is here in which Nabokov's work is so important. His work demonstrates how voice from the present about the past is evident. As Nabokov calls out for his "Memory" to "Speak," it becomes clear that this voice is seen through a modern prism. The work is so important because it represents how our past is our own, and yet it belongs to the present tense. We use the present tense to filter our own past through thematic designs. Nabokov's work demonstrates this importance. Memory is never absolute and beyond question. It is constantly filtered through the lens of the present tense, reflecting that the way in which our "memory speaks" is ongoing and ever changing. Nabokov's memoirs are important because it reflects how important it is to have our memory speak. It is a state of being that might change with time because we change with time. In being able to illuminate this philosophical reality, Nabokov's work is significantly important.