The phrase "a main theme of the" is correct and usable in written English.
It can be used when discussing the central idea or topic of a piece of writing, artwork, or any other form of expression.
Example: "In her novel, a main theme of the story is the struggle for identity in a changing world."
Alternatives: "a central theme of the" or "a primary theme of the".
The council's performance was a main theme of the discussions at the White House, several officials said.
I hope the viewer takes away a sense of isolation, which is a main theme of the play.
A main theme of the book was to emphasize the gigantic role that cultural evolution plays in making individuals different, and in making groups different.
This is, indeed, a main theme of the progressive master narrative: the 1% has grown so disproportionately powerful that it, for most practical purposes, owns "the system".
Asked by a joking reporter whether the commercial counted as an "in-kind contribution" from Mr. Eastwood, Jay Carney, Mr. Obama's press secretary, said it merely laid out the facts, and indeed the ad resembled a main theme of the president's State of the Union address last month.
A main theme of the behavioral finance literature is that many of the financial decisions we make are, in retrospect, unwise.
Clinton advisers say that pitting Mrs. Clinton and the voters, on one side, against Mr. Obama and Washington pundits will be a main theme of hers in the final primary contests.
A main theme of Kampung Boy is the contrast between the traditional rural way of life and the modern urban lifestyle.
A main theme of his work is the defeat of idealists and idealism.
Mr. Romney returned to a main theme of his campaign: that the mullahs had moved ahead with their program because "they saw weakness where they had expected to find American strength".
The liquor issue pitted wets and drys in stable uncompromising coalitions that formed a main theme of Hoosier politics into the 1930s.
