The poem sets two very different kinds of beginning side by side. One is quiet and natural: a pear coming into being, the first small sign of fruit as summer starts. The other is loud and human: a crowd in the park, singing anthems and lighting fireworks to celebrate the night.
The odd phrasing is what makes it interesting. The pear is born "out of each anthem," as if the songs themselves could produce something living and ripening. That suggests the speaker sees the noise of the celebration and the slow growth of nature as connected, not opposed. The fireworks flash and vanish, while the pear will keep growing.
The speaker never says how they feel outright. The tone is observant, a little dreamy and wondering. The mood is warm and open, full of the excitement of a summer night, but with a calm, gentle curiosity underneath it. The line breaks, with "where all" set apart on the page, give the sense of a crowd gathering and spreading out.