The aesthetic importance of sublimity is discussed by Longinus in Section IX of his treatise. In this section Longinus discusses the first essential source of elevated language, which, in his words, can be defined as "elevation of mind." This quality is only possible through the following injunction:

We must, therefore... nurture our souls... to thoughts sublime, and make them always pregnant, so to say, with noble inspiration.

"Noble inspiration" is vital to achieve because the aesthetic principles of sublimity can only be secured when it is "free from low and ignoble thoughts." There is a beauty in sublimity that makes it "admirable and worthy of immortality." Sublimity is something that is very closely linked to aesthetic principles of beauty and the ability to help humans transcend their limitations through a recognition of what is elevated and divine; it points the reader in other words to true examples of beauty as expressed in literature and the reader is transported as a result of surveying this beauty. Note the way in which Longinus describes sublimity as a state that is akin to producing a sensation similar to flight in its reader. This is only possible through the capture of the essence of beauty in its description.

Please define Longinus' concept of sublimity as stated in On the Sublime.

Longinus equates sublimity with elevation of the soul and attributes the presence of elevation to five sources, further asserting that the sublime elevates the audience's souls and originates in the poet's soul because of an innate ability in, or inherent capacity for, sublimity. Longinus depicts the circumstance of the sublime as an avenue that originates with innate qualities of soul in the poet and imbues the poetry with sublimity that the audience hears to the affect of being elevated with sublimity of their own.
The sublime is synonymous with elevation, which is defined as nobleness, grandeur and loftiness of thought and feeling, and dignity.

The five sources of the sublime (of elevation) are from the innate inner qualities of the poet as well as the well-honed skill of the poet. The sources from within are an inspired passion and grandeur and loftiness of thought. The sources of skill are masterful use of rhetorical elements; dignified, noble diction, which encompasses phrasing; and inspiring poetic structure. By this, it is seen that Longinus depicts the poet as the most skilled in language structuring and the most elevated in thought and feeling. Longinus had a welcomed reception among Elizabethans after the rediscovery and printed edition of his work in 1554 and a later equally warm reception among the Romantics.

What does Longinus discuss in On The Sublime?

The focus of this work, supposedly written by Longinus, although the majority of critics believe that it would have been another author who penned this work of early criticism, is the characteristics of sublime literature. These, the author lists and explores in turn. This text begins with a discussion about the relationship between "nature" and "art," or natural genius and learnt skills and talents. Having stated that natural genius is essential for sublime literature to be produced, but that this must also be coupled with "art" in the form of learnt skill, Longinus goes on to state the requisites of sublime literature, which can be identified in the impact such work has on the reader:

For, as if instinctively, our soul is uplifted by the true sublime; it takes a proud flight, and is filled with joy and vaunting, as though it had itself produced what it has heard.

Sublime literature, therefore, which is the focus of this early piece of literary criticism, is above all recognised by the emotional impact that it has on the audience. Longinus then states that there are five sources of "elevated language": creativity, passion, the use of figures of expression, noble diction and finally dignified composition. He then explores each in turn and looks at examples of what constitutes "sublime" literature and what does not.