Percy Bysshe Shelley's poem "To a Skylark" offers many different images and ideas with which one could contrast human limitations to the perception the poet offers of the skylark.
To begin, the skylark is able to fly: "Higher still and higher / From the earth thou springest" (lines 6-7). Here, the speaker is acknowledging the fact that the skylark is able to fly very high. Contrastingly, by stating that the bird can fly, the speaker is acknowledging the fact that humans cannot fly.
Another contrast the narrator establishes is the fact that the skylark's "voice" is able to be heard through "all the earth and air" (26). Although no longer true, given the expansion of technology, the speaker is unmistakeably stating that humans' voices are limited.
At the end of the poem, the speaker admits that the skylark is "better than all treasures / That in books are found" (98-99). Here, the speaker is illuminating the fact that the skylark can teach things to humankind that "we" cannot teach ourselves. Essentially, the skylark, for the speaker, is the ultimate educator, poet, singer, and being. In comparison to the skylark, humans possess nothing comparable.