1. Narrator vs The Poet
The narrator's poem, like all poetry, has resulted in a progress towards self-knowledge: Alastor is a dramatisation of this progress. The narrator develops from one kind of death to another, from the death of those who feel no void within themselves, to the death of his hero, whose consciousness of this void leaves him suicidal. The narrator, aroused from one extreme, has created a fiction which precipitates him into the other. By the end of the poem he is sunk in 'pale despair and cold tranquillity,' exactly in the situation of his hero when he lay down to die. Shelley's preface describes only two kinds of people; those whose 'self-centred seclusion' brings them to speedy ruin, and the others, worse than they, the 'selfish, blind and torpid' who feel within themselves no insufficient void. In writing his poem the narrator has extricated himself but has succeeded only in joining the first category, in becoming one with his hero. He has progressed from selfishness to solipsism, from one kind of death to another. He is unable to take that further step which Shelley accomplishes so elegantly in his Essay on Love. He becomes a prisoner of his own fiction, the solipsistic world of mirrors in which his hero lived, from which there is no escape but in death.(Richard Cronin, Shelley's Poetic Thoughts, p. 93)
2. Starting with a hymn, he ends with and elegy
Interestingly, the Narrator also describes the Visionary’s body as a “dream / Of youth，which night and time have quenched for ever"(lines 665-670). Dying with the Visionary are the Narrator’s former conceptions of his world. Through the course of his poem, the Narrator becomes increasingly dislocated from the Nature he praises at its beginning. Loss enters his vocabulary: starting with a hymn, he ends with an elegy. Such, perhaps, is what Shelley comes to see as the inevitable course of all poets of Nature. (Neil Freistat, "Poetic Quests and Questioning in Shelley's Alastor Collection" p.167)
3. Allusions to Wordsworth
Addressed in “To Wordsworth" as “Poet of Nature, the Wordsworth who weeps from learning that “things depart which never may return" is similarly elegiac (line 2); and in a chilling “correction" of the Intimations Ode that replaces a flower with a corpse, a deep joy with a profound sorrow, the Narrator contemplates the Visionary’s body with a “woe too ‘deep for tears' "(line 713). Left only with “pale despair and cold tranquillity" as his poem closes (line 718), the Narrator of “Alastor" like his protagonist, comes to inhabit a world devoid of promise. Nor are their parallel fates coincidental. (Neil Freistat p.168)
4. Shelley on the narrator and the poet
The Poet is left without hope and without despair. The narrator is left without hope. In the face of his despair he can only hope to imitate the Poet’s “cold tranquillity." That at least is the frame of mind he struggles to achieve at the end of Alastor, as he contemplates the difference the Poet’s life and death have made to his perception of the world. While the narrator is watching his hero, the author may be watching both hero and narrator with considerable urgency. Alastor is Shelley’s criticism both of Wordsworth’s “something far more deeply interfused" and of a purely transcendent idealism. In his hands these opposing (and related) points of view interact to produce a peculiarly painful sort of intellectual irony. By pitting one against the other Shelley exhausts the possibilities of both. Shelley was determined to see love as the only proper relation between subject and object. In Alastor he demonstrates, however, that if love is too simply conceived (as love of Nature or as desire for some perfectly knowable ideal) it results in nothing but frustration. (Norman Thurston, "Author, Narrator, and Hero in Shelley's Alastor," pp. 128-29)