What are the motifs in Dark Night of the Soul by St. John of the Cross?

Manna is a reoccurring idea in this book. The example of manna is one that St. John uses often in his description of the purgation of the soul. Manna was the food source for the Israelites while they wandered in the wilderness after they had escaped captivity in Egypt. This manna miraculously appeared each day for the people to gather and eat. In the book of Wisdom, which is part of the Catholic Bible, it is indicated that this manna could transform itself and taste like anything the eater wanted it to taste like.