Bridges on Proverbs 20:28
Charles Bridges on Proverbs 20:28

28.  Mercy and truth preserve the king: and his throne is upholden by mercy.
Punishment is indeed a necessary security against the infringement of the law. (Verse 26.) Yet a wise King will follow the example of the Great Sovereign, and “make judgment his strange work,” and mercy his “delight.”† And so long as truth inviolable is his guiding principle, the abuse of mercy need be little feared. Nay, mercy is the upholding pillar of his throne. (Isaiah 16:5.) But who does not know, that, while truth commands reverence, it is mercy that wins the heart? Solomon himself had a strong body-guard around him, for the safety of his person. (Song of Solomon 3:7.) Yet were the mercy and truth of his government not only the most splendid jewels of his crown, but ‘the best guard of his body, and supporters of his throne.’†
How lovely is this combination in the administration of the Great King! “Justice and judgment are the habitation of thy throne; mercy and truth shall go before thy face.” (Psalm 89:14.) Much more bright is the manifestation of these glorious perfections in that great work, by which he sacrificed even his Beloved Son, that man might be saved without the tarnish of one spot upon his infinitely adorable name. (Psalm 85:10.)