The Topic of a sentence
is the particular word or phrase on the page that the writer goes
on to say something about.
The Sentence Topic is often the grammatical subject of a sentence,
but not always. In this next sentence, the subject is "we,"
but the sentence is "about" the statute of limitations
(the topic is capitalized):
In regard to THE STATUTE OF LIMITATIONS, we must refer here to Squire.
The Sentence Topic is important to a reader's sense of coherence.
It establishes a point of reference for the rest of the sentence.
If that point of reference is clear, simple, direct, and familiar,
the reader starts out in familiar territory. If that point of reference –
the topic – is long, complex, abstract,and new, the reader
will be confused.