Beauty: the central theme of his poetry
The contemplation of beauty is the central theme of Keats' poetry. But it is his disinterested love for it that created a difference from the other Romantic writers and makes him the forerunner of writers like Oscar Wilde and the Aesthetes who saw in the cult of beauty the expression of the principle "art for art's sake", but, in Keats' view it's still a Romantic feature because of its moral aim. It is the classical Greek world that inspires Keats. To him the expression of beauty is the ideal of all art as the Greek beliefs. Keats identifies beauty and truth as the only type of knowledge; he says in the "Ode on a Grecian Urn": <Beauty is truth, truth beauty, -that is all Ye know on earth, and all ye need to know>.
Physical beauty and spiritual beauty
His first approach of beauty comes from the senses, from the concrete physical sensations. For Wordsworth only sight and hearing but for Keats all the senses are very important. This "physical beauty" is in all the forms of nature, in its colours, in its perfumes, in a woman, so beauty seen in all its details which produces much more joy. Keats says in the opening line of Endymion: <A thing of beauty is a joy for ever>, so this opinion introduces a sort of "spiritual beauty", that is the one of love, friendship and poetry. These two kind of beauty are linked together: the first one is linked to life and death, the second one is related to eternity.