What is the theme of In Memoriam AHH?

In Memoriam A.H.H. is a long reflective poem by Alfred, Lord Tennyson, written to commemorate his friend Arthur Henry Hallam, who died of cerebral hemorrhage in 1833 at the age of 22. The poem was published in 1850, seventeen years after Hallam's death. The poem reflects Tennyson's grief over Hallam's death and explores themes such as the nature of death, the immortality of the soul, the role of memory and the search for consolation in the face of loss.