It's a good idea to check for recurring to understand how they affect the overall of the text.

what goes in those blanks?

The two words are

Explanation:

A Motif is an element which reoccurs frequently througout a text or art work that is central it.

A theme in literature is simply the big idea, central message or underlying message of a lieteray work.

Thus, fixing the words into the sentence we have:

It's a good idea to check for recurring motifs to understand how they affect the overall theme of the text.

Cheers!

we need the passage first

that is true because that is something they fulfill for their work.