Poetry is at bottom a criticism of life.

In his poetry as well as in his life Shelley was indeed 'a beautiful and ineffectual angel', beating in the void his luminous wings in vain

Ah, love, let us be true
To one another! for the world, which seems
To lie before us like a land of dreams,
So various, so beautiful, so new,
Hath really neither joy, nor love, nor light,
Nor certitude, nor peace, nor help for pain;
And we are here as on a darkling plain
Swept with confused alarms of struggle and flight,
Where ignorant armies clash by night.

Poetry is simply the most beautiful, impressive, and widely effective mode of saying things

The grand style arises in poetry, when a noble nature, treats with simplicity or with severity a serious subject

Up the still, glistening beaches,
Up the creeks we will hie,
Over banks of bright seaweed
The ebb-tide leaves dry.
We will gaze, from the sand-hills,
At the white, sleeping town;
At the church on the hill-side—
And then come back down.
Singing: "There dwells a loved one,
But cruel is she!
She left lonely for ever
The kings of the sea.

(from poem 'The Forsaken Merman')