Including old post in current post

Can anyone suggest a way for me to do this:
I want to instead of linking to a previous post, completely pull it in. It needs to be linked though, not copied so if original post is updated all the other places it was pulled into are updated too.

To give you an idea of what I am trying to do it’s a how to site. So I will have a post how to turn off power to a circuit. Later I’ll make a post about adding an outlet. I’ll start by pulling in my turning circuit off post then type the adding outlet instructions. If down the road I improve my how to turn power off how to it should also update in the adding an outlet post.

Thanks for any help you can provide.