What were the major contributions of Longinus' On the Sublime to the history of literary criticism?

Longinus regarded the sublime as a thing of spirit, a
spark leaping from writer to reader, rather than a  product of technique.  He lists five
sources of the sublime, the first two of which--great thoughts and noble feelings--are
gifts of nature and the last three of which --lofty fiures, speech, diction and
arrangement--are products of art. 

Longinus identified five
sources of the sublime:

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"the power of forming great
conceptions";
"vehement and inspired passion";
"the due formation of
figures";
"noble diction"; and
"dignified and elevated
composition."

Correspondingly,
he highlights three problem areas to avoid while seeking the
sublime:

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Tumidity (overblown language)
Puerility
(hair splitting) and Parenthyrsus (false
passion)

In essence, he
realizes the same great men who produce great ideas will, by nature of their 'greatness'
also be capable of deep and sincere feeling.

To achieve
this end, Longinus believed in expressing thoughts and feelings via noble language ("due
formation of figures"), all of which is designed to elevate the individual into the
transdecent: "a figure is at its best when the very fact that it is a figure escapes
attention." 

To achieve this "formation of figures" there
are six figure types:

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amplification
inversions of word
order
polyptota--accumulations, variations, and
climaxes
particulars combined from the plural to the
singular
interchange of persons--addressing the audience as
"you"
periphrasis (circumlocution)--wordiness, circling
around the issue

Hope that
helps.