When viewing a site on a 4k monitors, things will either look great, or really bad. To ensure your content isn't drastically spaced out on the screen (making it hard to read), it's safe to wrap it inside of a container.
Wrapping your content in a container will make sure it always maintains a particular width no matter how large a users screen is, this makes your content easier to digest and read, and in return, makes your site look more professional by default.
This video will show you how to use an emulator within Chrome to simulate large screen sizes, and then show you how to make to make a container which keeps your text legible and easy to read.