Falling from gracious boughs, I sweetly call to mind, were flowers in a rain upon her bosom, and she was sitting there humble in such glory now covered in a shower of love's blooms: a flower falling on her lap, some fell on her blond curls, like pearls set into gold, they seemed to me that day; some fell to rest on ground, some on the water, and some in lovelike wandering were circling down and saying, "Here Love reigns."
After embracing the idea of his own death, Petrarch pulls a 180 and resumes his besotted admiration of Laura.
Once again, we're on the banks of the river watching the flower petals fall and bedeck her gorgeous chest and her, erm, lap. Naturally, she has blonde curls.
Petrarch has a habit of staring at Laura a lot, and giving us little tidbits of descriptions of her. You may have noticed this. But he doesn't really give a comprehensive look at her face or body. He observes her walk, manner, hair color, her smile, her robe—but it's not exactly a portrait. When Petrarch does this—and compares her traits through metaphor or simile—he's creating a blason(a literary device that Petrarch's Canzoniere makes popular).
So in stanza 4, we get a partial blason that invites us to join in Petrarch's admiration. The flowers land on her breasts, as though beauty attracts beauty. Laura's "blond curls" are also ornamented by the wayward flowers, so that the whole effect is "like pearls set in gold" (48). We can't really know what she looks like, but we know she looks good to Petrarch. In the final line, he tells us that Laura belongs to the court of King Love (i.e., she was made to play the game of love).
Stanza 4 is quiet and regular, poetically speaking. There are no fireworks here. That's not surprising, though, since Petrarch has fallen back into his reverie on the beautiful Laura.