What is a word that means a unifying or a dominant idea?

Question

My daughter asked me this for her homework, but I can not help her, since English is not my first language.

Answer 1

It depends on the context. The first sounds most literally correct by your question.

theme: "a unifying or dominant idea, motif, etc., as in a work of art."

thesis: "a subject for a composition or essay."

creed: "any system, doctrine, or formula of religious belief, as of a denomination."

Answer 2

Dominant=commanding, controling or prevailing

Answer 3

thesis or theme??