Explain the difference between unilinealism and diffusion.

Unilinealism is the social theory in which different social status is aligned in a single line that moves from most primitive to most civilized.

and

Diffusion is the spreading of something more widely.

Explanation:

so the answer is that Unilinealism is social theory, and Diffusion is just a spreading... nothing more, nothing less!

must repent and believe in god.

or the book

journey across time - chapter 10 "the rise of christianity"

here is a link that will you.