Trying to understand twentyfourteen theme source code

Pretty simple. is_front_page() checks to see if the page being displayed is the main blog page, and twenty fourteen_has_featured_posts() is a function defined in functions.php that checks whether or not there are any featured posts. You can define which posts should be considered featured posts in your Dashboard, under Appearance > Customizer. If both of those conditions are true, then get_template_part() loads a file named featured-content.php.

You mentioned that you don’t see any changes when you remove those lines. What are you trying to do?

Nothing was changing, may be because there is not featured-post.