The speaker is a religious man who has read and absorbed the Christian scriptures. He talks like a priest or preacher. He isn't simply content to quote or recite scripture; he takes his inspiration from the Book of Psalms, but turns his attention to the specific qualities of nature. He looks at nature almost like a biologist.
You could imagine the speaker as the kind of person who collects samples to add to his personal collection, such as a bird's feather or a particularly colorful stone. You might see him sitting underneath a tree with a notebook and making sketches of the "dappled things" he has seen. Indeed, the word "stipple" (line 3) is a term from drawing. He always notices the unusual or eccentric features of the landscape. He is very pious, and he wants you to be pious, too. He thinks that merely describing the world as it is should be enough to give people a sense for the mysteries of spiritual life, and would lead naturally to praising God.