Question

What can a motif contribute to, or become, when it gathers larger significance throughout a text?

Answer 1

When a motif gains larger significance throughout a text, it becomes a theme, something larger that you talk about in your work. But since theme is not a listed option, I would say the correct answer is 5) a thesis. 

Answer 2

The answer is 5: a thesis

 The repetition of a specific theme dominanting of things that have a significance in a literary work is what this literay device, motif, is about. It helps to develop the central theme.  And, being a recorring element, it can be used as a reminder of certain ideas for the readers; it's like the claim or main argument about a topic.