Stanza 1 Summary

Get out the microscope, because we’re going through this poem line-by-line.

Hail to thee, blithe Spirit!

Shelley starts out big here. This isn't a quiet, subtle opening line. It's more like a joyful shout. When a poet calls out to something like a bird, without expecting it to talk back, we call that an apostrophe. (For some reason they gave this figure of speech the same name as the little mark that goes before the s in most possessive words. Go figure.) See our "Symbols, Imagery, Analogy" section for more on that technique.
Vocab note: the word "blithe" is a kind of old-fashioned term that means carefree, happy, lighthearted.
We think the use of the word "Spirit" here is really important. (Shelley gives us a hint by capitalizing this word and a few other key terms in the poem.) It tips us off right away that this is more than just a simple nature poem. How much more? Let's read on…

Bird thou never wert

Now Shelley explains a little more about why he calls the bird a "Spirit." In fact, he says here that this bird isn't a bird at all, and never has been. (The phrase "thou never wert" is a fancy way of saying "you never were.")
The skylark in this poem is something more than just a chirpy, pretty little bird. It's connected to the spirit world, and to all kinds of other happy, beautiful things, like heaven, color, light, and the sky.
We'll work through all the other things the skylark is connected to as we get to them, but right now, it's most important to know that this is one special, supernatural bird

That from Heaven, or near it,

Here's a little more about this super-cool bird. It's not just up in the sky, it's in "Heaven, or near it." Notice that capitalization again—"Heaven" is another big term, which suggests that there's something holy (or almost holy) about this bird.
You might also have noticed that "near it" rhymes with "spirit" at the end of line 1. So, we know now that this poem rhymes, and we're starting to see how.
Check out our "Form and Meter" section for the full story.

Pourest thy full heart

This little bird is pouring out its heart from heaven, or at least that's what our speaker hears. It's not just singing, it's expressing its emotions.
The speaker doesn't just come out and say that this bird (or this "Spirit") has feelings like a person, but he's hinting at that. When you give an animal or a thing human qualities, we call that personification.
Bottom line: most birds don't pour their hearts out, but this one does. Remember, this is a special bird.

In profuse strains of unpremeditated art.

We get a few tricky words in here, so let's nail those down first:
"Profuse" just means that there's a lot of something; it's abundant. "Strains" are pieces of music, passages of melody. And "unpremeditated" means not planned in advance.
So, putting that all together, it means that this bird sings a lot of little improvised melodies.
That last phrase "unpremeditated art" is really important. Just like the speaker is making art in this poem, the skylark is too. Except he doesn't have to think about it—the art of nature just comes spilling out on its own.
That kind of idea, about the art and the feeling that lives in nature, was the kind of thing that got the Romantic Poets really excited.