Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

3 The heavens in height, and the earth in depth, And the heart of kings are unsearchable. This is a proverb in the priamel-form, vid., p. 13. The praeambulum consists of three subjects to which the predicate אין חקר [= no searching out] is common. "As it is impossible to search through the heavens and through the earth, so it is also impossible to search the hearts of common men (like the earth), and the hearts of kings (like the heavens)" (Fleischer). The meaning, however, is simple. Three unsearchable things are placed together: the heavens, with reference to their height, stretching into the impenetrable distance; the earth, in respect to its depth, reaching down into the immeasurable abyss; and the heart of kings - it is this third thing which the proverb particularly aims at - which in themselves, and especially with that which goes on in their depths, are impenetrable and unsearchable. The proverb is a warning against the delusion of being flattered by the favour of the king, which may, before one thinks of it, be withdrawn or changed even into the contrary; and a counsel to one to take heed to his words and acts, and to see to it that he is influenced by higher motives than by the fallacious calculation of the impression on the view and disposition of the king. The ל in both cases is the expression of the reverence, as e.g., at Ch2 9:22. וארץ, not = והארץ, but like Isa 26:19; Isa 65:17, for וארץ, which generally occurs only in the st. constr.