The main theme of the poem "Ring Out, Wild Bells" by Alfred, Lord Tennyson is Renewal. This is apparent in the opening stanza where the poet writes:
The year is dying in the night;
Ring out, wild bells, and let him die
The poem is a discourse on new beginnings - a fresh start for mankind as a whole, and individuals in particular. There is a call for Truth in this poem - a doing away once and for all with falsehood and embracing the dignity and purity of truth.
At its core, "Ring Out, Wild Bells" is an energetic cry for human beings to dispense with destructive ideologies and beliefs that lead to destructive actions across the board, as pertains to the human experience. A spiritual renewal must first take place within the mind of human beings. Only then can other types of renewal take place, including the physical renewal of the earth from the destructive effects of war and other harmful events.
Tennyson calls for an end to grief for those who have died. They are at rest; we who remain must move on and live. He also calls for and end to class strife, desiring rich and poor (and all classes in between) to live in harmony with one another.
The renewal that Tennyson calls for is one where the old order and way of thinking and doing things is banished for good. The poet desires an end to political strife. He wants the proper rule of law, in tandem with good manners - people treating others with respect as they all work for the common good in society.
Tennyson also desires a renewal in health, both physically and in the inner man. He speaks of mankind ringing out the "old shapes of foul disease" as well as ringing out greed. The renewal he talks about will rejuvenate man, society and the earth.
In the end, Tennyson knows all of the above listed here is a tall order for human beings to accomplish. Therefore, he calls on the One whom he believes will accomplish complete Renewal for mankind:
Ring in the Christ that is to be.