What is the theme of the poem "An Apology for Using the Word "Heart" in Too Many Poems"?

No doubt a student has read a poem in which the word
death or heart appears many times. It seems to
the student that poets only write about either love or death as if those are the only
two emtions that humans have. This poem is the author's response to that assumption.
This poem professes to be an “apology,” which might mean either a defense or an
explanation of why the poet should regret using the word “heart” too often, with the
possible promise not to use the word again. Most of the poem draws the reader’s
attention to a variety of interpretations of the meaning of “heart,” with the climax of
these definitions being reached in lines 27–28: “the capacity to love in the fullest /
Sense.”