In the second and third stanzas, he examines the picture of the piper playing to his lover beneath the trees. Here, the speaker tries to imagine what the experience of the figures on the urn must be like; he tries to identify with them. He is tempted by their escape from temporality and attracted to the eternal newness of the piper’s unheard song and the eternally unchanging beauty of his lover. He thinks that their love is “far above” all transient human passion, which, in its sexual expression, inevitably leads to an abatement of intensity—when passion is satisfied, all that remains is a wearied physicality: a sorrowful heart, a “burning forehead,” and a “parching tongue.” His recollection of these conditions seems to remind the speaker that he is inescapably subject to them, and he abandons his attempt to identify with the figures on the urn.
In the fourth stanza, the speaker attempts to think about the figures on the urn as though they were experiencing human time, imagining that their procession has an origin (the “little town”) and a destination (the “green altar”). But all he can think is that the town will forever be deserted: If these people have left their origin, they will never return to it. In this sense he confronts head-on the limits of static art; if it is impossible to learn from the urn the whos and wheres of the “real story” in the first stanza, it is impossible ever to know the origin and the destination of the figures on the urn in the fourth.
It is true that the speaker shows a certain kind of progress in his successive attempts to engage with the urn. His idle curiosity in the first attempt gives way to a more deeply felt identification in the second, and in the third, the speaker leaves his own concerns behind and thinks of the processional purely on its own terms, thinking of the “little town” with a real and generous feeling. But each attempt ultimately ends in failure. The third attempt fails simply because there is nothing more to say—once the speaker confronts the silence and eternal emptiness of the little town, he has reached the limit of static art; on this subject, at least, there is nothing more the urn can tell him.
In the final stanza, the speaker presents the conclusions drawn from his three attempts to engage with the urn. He is overwhelmed by its existence outside of temporal change, with its ability to “tease” him “out of thought / As doth eternity.” If human life is a succession of “hungry generations,” as the speaker suggests in “Nightingale,” the urn is a separate and self-contained world. It can be a “friend to man,” as the speaker says, but it cannot be mortal; the kind of aesthetic connection the speaker experiences with the urn is ultimately insufficient to human life.
The final two lines, in which the speaker imagines the urn speaking its message to mankind—”Beauty is truth, truth beauty,” have proved among the most difficult to interpret in the Keats canon. After the urn utters the enigmatic phrase “Beauty is truth, truth beauty,” no one can say for sure who “speaks” the conclusion, “that is all / Ye know on earth, and all ye need to know.” It could be the speaker addressing the urn, and it could be the urn addressing mankind. If it is the speaker addressing the urn, then it would seem to indicate his awareness of its limitations: The urn may not need to know anything beyond the equation of beauty and truth, but the complications of human life make it impossible for such a simple and self-contained phrase to express sufficiently anything about necessary human knowledge. If it is the urn addressing mankind, then the phrase has rather the weight of an important lesson, as though beyond all the complications of human life, all human beings need to know on earth is that beauty and truth are one and the same. It is largely a matter of personal interpretation which reading to accept.