A.N-I'm not sure if this would qualify as a Royal psalm, but oh well.
Royal Psalm
A king reigns on
Earth,
You reign in Heaven.
You whisper words in a ruler's
heart,
and fill his head with
wisdom.
Whether he follows is his will,
but You know.
A king is but
a mere
ambassador,
Your servant to command.
The kingdoms of Earth
are Yours
to do with as You please.
If kings are wise, they will follow
You.
Make, then, your ambassadors
wise,
to honor your rightly