I know that button titles shouldn't just be "Okay", "Yes" or "No", but be the name of the specific action the button will perform. What about the message itself?

For example, I display this modal alert to the user: " is missing content that it needs to run" with a button that says "Update Content"

Should it be titlecase? Should it have a period at the end? How pithy should the message be? I personally dislike long dialogs, but is this best for the end user?