24. Ignorance of things, too, renders figurative expressions obscure, as when we do not know the nature of the animals, or minerals, or plants, which are frequently referred to in Scripture by way of comparison. The fact so well known about the serpent, for example, that to protect its head it will present its whole body to its assailants -- how much light it throws upon the meaning of our Lord's command, that we should be wise as serpents; that is to say, that for the sake of our head, which is Christ, we should willingly offer our body to the persecutors, lest the Christian faith should, as it were, be destroyed in us, if to save the body we deny our God! Or again, the statement that the serpent gets rid of its old skin by squeezing itself through a narrow hole, and thus acquires new strength -- how appropriately it fits in with the direction to imitate the wisdom of the serpent, and to put off the old man, as the apostle says, that we may put on the new; and to put it off, too, by coming through a narrow place, according to the saying of our Lord, "Enter ye in at the strait gate!" As, then, knowledge of the nature of the serpent throws light upon many metaphors which Scripture is accustomed to draw from that animal, so ignorance of other animals, which are no less frequently mentioned by way of comparison, is a very great drawback to the reader. And so in regard to minerals and plants: knowledge of the carbuncle, for instance, which shines in the dark, throws light upon many of the dark places in books too, where it is used metaphorically; and ignorance of the beryl or the adamant often shuts the doors of knowledge. And the only reason why we find it easy to understand that perpetual peace is indicated by the olive branch which the dove brought with it when it returned to the ark, is that we know both that the smooth touch of olive oil is not easily spoiled by a fluid of another kind, and that the tree itself is an evergreen. Many, again, by reason of their ignorance of hyssop, not knowing the virtue it has in cleansing the lungs, nor the power it is said to have of piercing rocks with its roots, although it is a small and insignificant plant, cannot make out why it is said, Purge me with hyssop, and I shall be clean".