Albert Barnes Commentary Proverbs 30:5

"Every word of God is tried: He is a shield unto them that take refuge in him." — Proverbs 30:5 (ASV)

Out of this consciousness of the impotence of all humanity's efforts in pursuit of the knowledge of God arises the sense of the preciousness of every living word that God Himself has revealed, whether through “the Law and the prophets” or through “wise men and scribes.”