Both poems essentially focus on the ideal of the artist/poet to indulge his/her talent and find inspiration in nature. It seems though, that Keat's poem focuses more on a universal theme: man's disregard and neglect of nature, a common theme in Romantic poetry, whereas Tennyson's poem focuses on the artist and his/her fear of losing touch with his/her talent when he/she becomes part of 'common society'.
Keat's spoke out against the drudgery created by the Industrial Revolution and sought to inspire his readers to admire and respect nature and to find solace and inspiration in its beauty. His poetry asks us to rekindle our relationship with all that is natural and to be inspired by it. For him the true artist's talent lies in his/her exploration and appraisal of whatever is found in nature. Man needs to focus on the natural and reject the materialistic and mundane. In nature we discover our true worth and reconnect with our true selves.
It is clear in this poem that Keat's plea is for man to be inspired by the eternal ocean and its beauty. However, it seems that man is ruled by convention and the norms of society. Keat's wants us to rediscover our inner selves and not be guided extemporaneous and fake factors.
In a similar vein, The Lady of Shallot represents the artist, who finds his/her greatest inspiration within herself - that which is natural. This is why she is secluded and lives in her drab grey castle, looking at the world through a mirror. It is clear that Tennyson implies here that what the artist perceives about the world can only be but a shadow of what is real. The true reality lies within.
The Lady of Shallot is forbidden through a curse to indulge with the rest of society, in even the most mundane of activities. If she should participate, she would die. For Tennyson, this is the artist's curse - he or she should be driven by a deeper, inner sense, only then would the artist be truly inspired. This is evident from the fact that once the Lady of Shallot leaves the protection of her castle and is drawn to the attraction inspired by Lancelot, she dies. For Tennyson, the death of the artist and his/her ability is caused by his/her seeking out and embracing the external, that which is conventional, but not natural.
It is clear, therefore, that both poets wish to inspire us to indulge in what is natural and live beyond the materialism and conventions imposed upon us by society. Only then will we be truly inspired.