An author is never the “speaker” of his poem but rather constructs a voice, a persona, which acts as the speaker.  It is similar to an actor playing a part:  the person who is the actor and the character he portrays are not the same.  There are many figures of speech in the poem, both metaphors and similes. These include “deaf heaven” and “bootless cries.”  The former personifies heaven, suggesting that no one hears what the speaker has to say, and the latter metaphor also is a personification, suggesting the speaker is poor, so that his cries are bootless. “Then my state, / Like to the lark” is a simile that expresses his state of mind becomes joyful when the speaker thinks of his good friend. “Sullen earth” is another metaphor that, by personifying earth (it has a sullen mood), indicates the sad state from which he changes by the thought of his good friend. Symbols have wider ranges of meaning than the figures of speech that dominate this poem, although some of the metaphors might move beyond mere comparisons into the range of symbol. In this way, perhaps “kings” at the end of the poem can be said to symbolize all fortunate people, and “lark” symbolizes joy and happiness. The line between metaphor and symbol is often fine.