How does poetry evoke change and emotion

In Percy Bysshe Shelley’s essay “A Defence of Poetry,” the author discusses the different aspects of the literary genre that make it so impactful.
One of these is poetry’s ability to create change. Shelley discusses this in the last several paragraphs of the essay.
He introduces this idea in the following quote:

The most unfailing herald, companion, and follower of the awakening of a great people to work a beneficial change in opinion or institution, is poetry.

This quote suggests that at any time in which progress in society occurs, one will find a particular change in the poetry of the time. According to Shelley, art doesn’t imitate life but rather shapes it.
He states that anyone who reads the poetry written at the time can feel the “electric life which burns within [the authors’] words.” The passion with which a poet imbues his or her work transfers to the reader; as a result, the reader becomes inspired to conform his or her world to the idealized version presented in the poem.
In his final statement at the end of the essay, Shelley explains why people enjoy poetry:

Poets are the hierophants of an unapprehended inspiration; the mirrors of the gigantic shadows which futurity casts upon the present; the words which express what they understand not; the trumpets which sing to battle, and feel not what they inspire; the influence which is moved not, but moves. Poets are the unacknowledged legislators of the world.

In Shelley’s view, poetry voices what the average person cannot articulate and thereby serves as a source of inspiration. People find the courage to change things because of the passion and enthusiasm transferred from poet to reader.