Let's say you are preparing to teach on Sunday class, and the theme of the day is related to the three readings of that Sunday. Unfortunately, there are many biblical texts of the Sunday readings that you are not sure if you understand them correctly. What would you do ? Would you call your priest ? What if he's busy with a funeral Mass or can't help you for other reasons ? Your best bet would be to have a good set of Bible commentaries. Please take a look at my section on "Bible Study" for a few suggestions of Bible commentaries. If you have the 19 volumes of the Navarre Bible, you're in good shape. If not, get this Douay-Rheims Bible with Father Haydock's Notes. It features a lot of good commentaries in one single volume.