Sonnet 55's tone is one of somber celebration, appropriate for praising someone of high status. All of the poet's allusions are solemn and concerned with death. "Gilded monuments" are built after the princes referred to have died, and war is a primary instrument of death.
But Shakespeare writes the verse to literally immortalize his subject, saying that none of the ravages of time or conflict can erase the praiseworthiness of the one referenced. What is interesting here is the final couplet. Although the rest of the sonnet could easily refer to the poet's patron, or some high official, the final line, "You live in this, and dwell in lovers' eyes" seems to indicate that, instead, it refers to a romantic object. The line is, in fact, in contrast with the rest of the sonnet, and we continue to speculate why Shakespeare would choose to comment on a personal relationship so formally.