The poem begins with its speaker recalling a low point in their life. The speaker is never named or gendered: they might be a stand-in for the poet or a separate persona entirely.
The speaker recalls lying down somewhere indoors, "Full of desire" for some unnamed person or thing. As they watch the scene outdoors, presumably through a window, they take no comfort from anything in nature.
In fact, nature seems hostile, mocking, and superior. The speaker recalls "the sky wounding me" in some metaphorical way—perhaps with its piercing brightness, perhaps with its cold indifference. Meanwhile, "Each cloud" in that sky reminds the speaker of "a ship without me sailing"; in other words, it makes the speaker feel abandoned, or as if they're missing out on some grand adventure. "Each tree" in the landscape seems to "Possess" what the speaker's "soul lack[s]," and wishes for most: "tranquillity." In other words, while the speaker's in turmoil, the trees seem calmly at ease.
This attribution of human feelings to nature is called the pathetic fallacy, and it's an early example of the speaker's tendency to personify or anthropomorphize the natural world around them. Even when they feel alone and detached from nature, as they do here, they view nature as remarkably human.
The second stanza reveals the root cause of all this distress: "heartbreak." The speaker has been through a breakup and isn't over their ex. They find themselves in a classic post-breakup situation: "Waiting for the longed-for voice to speak / Through the mute telephone." Of course, the call never comes, and the speaker's "body" feels "weak" with "heartbreak"—which they call "the well-known and mortal death." That is, heartbreak is an old and storied feeling, and it feels like death in life.
These first six lines establish the form that the rest of the poem will follow: tercet stanzas rhyming AAA, BBB, and so on. The consistent structure gives the poem a balanced, harmonious quality, while the consistent end-stopping of stanzas (all end with periods) gives it a stately, measured pace. These qualities are at odds with the speaker's initial turmoil, but they suit what will be the dominant mood of the poem: confident, "Passion[ate]" appreciation for the world.