"make a garden” for Mattie..."
See in text (Chapter IV)
We can consider Ethan’s desire to construct a garden for Mattie in relation to the Bible. In literature, the garden is often used as an allusion to the Garden of Eden in the book of Genesis. In Genesis, Adam and Eve are kicked out of the Garden of Eden for being unfaithful to their word or duty to God. Note further that this “garden” is not really a lush garden one might imagine—all he can do is plant geraniums.
"as dark as Egypt..."
See in text (Chapter V)
This common expression is a biblical allusion to the story of The Ten Plagues of Egypt in the book of Exodus. Darkness is the ninth plague that God inflicted on Egypt—a darkness that is extremely dense and impenetrable.