For the king trusteth in the LORD, and through the mercy of the most High he shall not be moved.
This verse, which speaks both of the King and of THE LORD, forms the transition from the address to God to the address to the king.
For the king trusteth in the Lord. The ground of the confident anticipation concerning the everlasting glory of the king is, that Yahweh is his trust, so that through the mercy (or love) of the Most High he shall not be moved.