This fragment of a verse come from a psalm that is magnifying what God does, and how he has protected Israel. And in the midst of this praise is this simple admonition. To be still. And to know that the Lord (YHWH) is God.
This psalm of David is a prayer for God’s presence and leading. It is the cry of a heart that yearns to know more and more of God. A heart that wants to know and follow his truth. A heart whose hope was not in power or strength of arms, but in God.