To see a World in a grain of sand,

And a Heaven in a wild flower,

Hold Infinity in the palm of your hand,

And Eternity in an hour.

After reading these lines, your attention gets hooked. In fact, this stanza is the tone-setter for the whole poem, and understanding it is also crucial to understanding the whole poem. David Pinching of Bibliomania.com gives an excellent analysis of the whole poem. I give part of his analysis below :

“There is a contemplative tone set up at the start of the poem in the famous lines:

“To see a World in a grain of sand,

And a Heaven in a wild flower,

Hold Infinity in the palm of your hand,

And Eternity in an hour.”

Here, Blake seems to be setting up the basic theme of the poem: of a nature visible in every thing, the microcosm expressing the macrocosm totally (i.e. the smaller thing demonstrating, even proving the greater thing). It is a positive image, too, in the immediate reference to Heaven and the image of the wild flower. This tone does not last. He continues, ………”

————————————————

My own simple interpretation to these opening lines is : There’s wisdom to be learned in the smallest of things, and their truths are as eternal as the Heavens. I put it as simple as that.