Wordsworth explicitly sets out to write verse in the kind of language used by ordinary people. This was a radical departure from the prevailing Neo-Classical orthodoxy, which held that poetry should be written in elevated language, in keeping with the classical models of verse it sought to emulate.
For Wordsworth, as with the Romantics in general, humankind was conceived of as an organic whole linked together by emotion. In writing poetry he sought to excite that emotion, making his work more truly universal than that of the Neo-Classicists, whose taste for universality was reflected in Platonic ideals that could only be grasped by an educated elite.
What's more, Wordsworth sets out his intention to write about the lives of ordinary people themselves. Once again, this represented a radical break with the Neo-Classicists, who thought such people unworthy subjects of what they considered an elevated art from dealing with universal truth, goodness, and beauty. As far as they were concerned, the lives of the poor, the ordinary country folk such as Wordsworth's leech-gatherer, could tell the discerning reader nothing about what was, in the Platonic sense, ultimately real.