"Mechanical reproduction of a work of art, however, represents something new" (Benjamin 1233)
The question then becomes what is it?
Benjamin throws a lot of history and terms at the reader which can boggle and distort; "aura" (Benjamin 1235) is of a clear interest, as well as other words like tradition and authority. While it might be safe to say that these choices in vocabulary hold a common, more colloquial meaning, Benjamin is using these words to help argue for this "new" device of art.
Namely, that mechanical reproduction/photography is a process that identifies a new cultural perception of the value system on art.
Mechanical reproduction can do several things that "old art" cannot: 1) "Process reproduction is more independent of the original than manual reproduction" (Benjamin 1234), it "can capture images which escape natural vision" (Benjamin 1235), and finally "put the copy of the original into situations which would be out of reach for the original itself" meeting the "beholder halfway" (Benjamin 1235).
Why these qualifications are brought up has less to do with aesthetics and more to do with their counterpoint in what Benjamin repeatedly refers to as "Aura" and its associations.
This independence from the original, in conjunction with its multiplicity (copies), puts the perception of "old art" as "authentic" or "authoritative" at risk. "The authenticity of a thing is the essence of all that is transmissible from its beginning, ranging from its substantive duration to its testimony to the history which it has experienced" (Benjamin 1235). Copies/reproduction then, act/s to do away with a historical authenticity; copies defy "birth" or "origin" which have great value and authority in "old art." This substitution of a "plurality of copies for a unique existence" (Benjamin 1235) is said to "wither" (Benjamin 1235) the "aura" in our current age. Aura then could be seen as attached to "old art" and another word- "tradition"- whose links emphasize an aging/dying cultural perception that birth, duration or lifespan, and an objects singularity in the realm of art bears greater significance (i.e the older the better; the more obscure the better; the less reproduced the better).
Since reproduction can both remove the object from its place in history/time/space and relocate it, effectively removes it from that "old art" perception, and instead "reactivates" (Benjamin 1235) the object for the beholder. Benjamin calls this a "shattering of tradition" whose most powerful "contemporary mass movement" agent is the film (Benjamin 1235); this agent that liquidates "the traditional value of cultural heritage" (Benjamin 1235).
Benjamin does not say that art is dying. To the contrary, its tradition is simply evolving. This new direction is characterized by a modern desire to "pry and object from its shell" (Benjamin 1236) and a perception "whose 'sense of the universal equality of things' has increased to such a degree that it extracts it even from a unique object by means of reproduction" (Benjamin 1236). A current value system of art then is not focused on "tradition" in its archaic sense, but rather its multiplicity, its nearness, its adjustment "to the masses and of the masses" (Benjamin 1236).