explanation about sheley's A defence of poetry?

In the essay, "A Defence of Poetry," Shelley argues that poetry brings about moral good. Poetry, Shelley argues, exercises and expands the imagination, and the imagination is the source of sympathy, compassion, and love, which rest on the ability to project oneself into the position of another person. He writes,

A man, to be greatly good, must imagine intensely and comprehensively; he must put himself in the place of another and of many others. The pains and pleasures of his species must become his own. The great instrument of moral good is the imagination; and poetry administers to the effect by acting upon the cause. Poetry enlarges the circumference of the imagination by replenishing it with thoughts of ever new delight, which have the power of attracting and assimilating to their own nature all other thoughts, and which form new intervals and interstices whose void forever craves fresh food. Poetry strengthens the faculty which is the organ of the moral nature of man, in the same manner as exercise strengthens a limb.

No other English poet of the early nineteenth century so emphasized the connection between beauty and goodness, or believed so avidly in the power of art’s sensual pleasures to improve society. Byron’s pose was one of amoral sensuousness, or of controversial rebelliousness; Keats believed in beauty and aesthetics for their own sake. But Shelley was able to believe that poetry makes people and society better; his poetry is suffused with this kind of inspired moral optimism, which he hoped would affect his readers sensuously, spiritually, and morally, all at the same time.