Jonathan secretly signaling David to flee by shooting an arrow — used as an analogy for the historical and mystical senses of Scripture
Preface and Praise of Sacred Scripture
Chapter III: On the Difficulty of Sacred Scripture— Used as an extended analogy: the arrow's immediate purpose (pick it up) vs. its deeper purpose (David should flee), paralleling the historical and mystical senses
"Jonathan in 1 Kings chapter 20... by shooting an arrow according to their agreement and ordering the boy who was to collect it to go farther ahead, he signified two things"