What is narrative pace?

Pacing is how quickly you let things happen in a story.
It would be a mistake to have everything happen all at once therefore the plot is inter spaced with moments of character building, back-story, philosophy, narrative and such so that the reader has an opportunity to experience a wealth of human interest.

'High Noon' is a western movie that follows an exact time-line. Every minute is the film corresponds to a minute in (what would be real life). It is realistically paced with plenty of human interaction and only a blurb of action at the very end.

'Flowers for Algernon' follows the pattern of a series of a daily reports. The book is paced as a post-day evaluation.

'The Color(sic) Purple' follows the pattern of a series of letters. It is paced on a monthly basis.