Psalm 45 is rather unique. It was originally composed as a wedding ode for a king and his bride.
The Psalmist celebrates the king and his reign with effusive praise, and also gives practical advice to his chosen bride. In this Psalm, we can see reflections of what God intends when His people, especially His chosen representative on earth - the King - use their powers and positions wisely. With this in mind, the author of Hebrews quotes from the strong language of this Psalm in Hebrews 1 to buttress his argument that Jesus is God in the flesh.