It depends on his background thus far. BFSU is designed to build understanding in logical systematic steps each building on what has gone before. If he has not had steps one and two, you cannot expect him to make much sense of step 3, even with help. I recommend starting with volume 1 then 2 and doing a review using the “Practices” section of each lesson. Only spend time on filling in ideas/concepts that he has missed or have fallen away. After this, you can be assured that he has the background or Volume 3.