God neither sleeps nor slumbers  -  Psalm 121:3

He will not suffer thy foot to be moved: he that keepeth thee will not slumber.

This verse guarantees the eternal security of those who trust in God. Since the foot speaks of foundation or standing, it means that God will keep us from slipping or falling. Because it is God that keeps us from slipping or falling, we are assured of stability, as our foot will be preserved, so that it will not be moved.