Your main assertion is a statement that presents your main interpretation of a text.
Your interpretation should look something like this:
The text (commercial, song, story, film, video game) suggests that main assertion
A few other ways of writing “suggests”:
reflects
implies
reveals
proposes
signifies
tells us
represents
Your main assertion should fit one of the following formulas:
Definitional/Categorical: (X is Y) or (X is not Y)
Resemblance: (X is like Y) or (X is not like Y)
Ethical: (X is right) or (X is wrong)
Evaluative: (X is a good Y) or (X is a bad Y)
Causal: (X causes Y) or (X does not cause Y)
Proposal: (We should do X) or (We should not do X)