Eccl. 4.9-12 tells us that two are better than one when it comes to labor, partnerships, and other practicalities. Older books and primary sources have a way of teaching us better than mediated works, which often fail. Secondary sources can, of course, greatly instruct by their analysis of things which we would not have noticed first hand. However, for the most part, I agree with Lewis that primary sources are easier to understand if we just read them on their own terms.
Nowhere is this more apparent than the bible versus commentaries and books about the bible. If one will read the bible on its own terms, with a desire to know and obey, they will reap more benefits than reading many books about the bible. Of course, the bible needs to be read as a whole to see the trees among the forest. Additionally, not everything will be clear upon the first or second reading. Some things may even allude us during this life. The bible is a complex book but the great bulk of it is very knowable if the reader will apply their hearts to a disciplined devotion of its contents.C. S. Lewis Preface to On the Incarnation – Credo Magazine