This isn't particularly good advice.
In writing the html for a page, you want to be as semantical as possible. Text should be in either p or h tags so as to have it formatted properly and to make the css clear for the next person who maintains it.
Spans can go inside of p tags, p tags can go inside of div tags. divs can not go inside p tags.
It is better to use a containing div for containing and use p's, h's and spans to control the text. That way you aren't adding extra divs to the code, and all of your p/h's can have general styling automatically.
Also, in html5 you typically wouldn't have text in a div unless you using content management to pull content from other places and have some sort of grid such as recent blogs or something like that. Otherwise text should be in sections, lists, or articles (or wrapped in a head tag).
Technically, there is nothing wrong with using div as a way to style text, semantically, it is not best practice.
Why bring this up? It's easier to start with good habits than bad and then learn the good.
