The Hebrew verb kashal means to stumble, totter, or fall — physically, morally, or spiritually. It describes the wavering of the wicked, the weakness of the weary, or the moral failure of those who depart from God's ways.
The contrast between those who stumble and those who are upheld is a recurring theme in Scripture. The wicked kashal in their iniquity (Proverbs 24:16), but the righteous rise again. Isaiah 40:30-31 promises that those who wait on the LORD will not stumble — they mount up with wings like eagles. Kashal also appears in prophetic warnings about the consequences of sin and apostasy.