The Hebrew verb kasaph means to long for, yearn intensely, or be pale with longing. Occurring 6 times in the OT, it shares its root with keseph (silver, H3701), possibly because silver was so precious people pined for it. The word captures an aching desire — the kind that changes a person's countenance.
Kasaph expresses the deepest form of spiritual longing. Jacob uses it of his longing for his family (Genesis 31:30). The Psalmist uses it of longing for God's courts (Psalm 84:2). This intense longing is presented as a virtue — the soul that aches for God, that pines for His presence and His salvation, is the soul rightly oriented. This word anticipates the beatitude of those who hunger and thirst for righteousness (Matthew 5:6).