If you view 2 John 1:9 and look at the MacArthur note, it says "see entry for:2 john 1:1 or 3 John 0:3"

3 John 0:3 :wow:

Chapter 0 is used for chapter introductions, so that's pretty normal.

Chapter "0" in commentaries generally refer to background, general, or explanatory notes about the book. Since there is no entry for the specific verse you are looking at, Mantis is telling you what the prior entry is and what the next entry is. In the case you reference, the commentary contains background such as author and date, background and setting, etc for 3 John, placed as Chapter 0, with specific "verses" containing the subheadings of background info.

Happy and profitable studying!

Ahhh sweet as. I did read that the MAC is being updated soon so hopefully the intro etc will be there in the update?

Thanks for your help!

The introductory material is already present. You can access it by clicking on the 3 John 0 link. When the link expand choose "jump to this verse" and you will see the entries. I hope you can find it.