Yahweh exhorts Joshua to keep the law and meditate (hagah) on it day and night (Joshua 1:7-8). The book is to be in his mouth constantly; like the prophets Ezekiel and John, he is to chew the book of the law for breakfast and dinner. Making the Word of Yahweh his food will lead to prosperity, success, conquest. We can reverse this: Eating books, Ezekiel and John are new Joshuas, the word-bread of God their provision for war.
The word “meditate” refers to a sound, the sound of muttering to oneself, the sound of whispered self-conversation. Or, the sound of a lion with its prey (Isaiah 31:4), the sound of thunder (Job 37:2), the sound of a harp (Psalm 9:17; 92:4) or of doves (Isaiah 38:14). Yahweh tells Joshua to growl over the word, protective as a lion; to rumble like a small thundercloud with the word in his mouth; to fill his mouth with the word so that he will become a musical instrument; to eat the book so that he coos like the dove of the Spirit.