Charles Ellicott Commentary Proverbs 8:9

"They are all plain to him that understandeth, And right to them that find knowledge." — Proverbs 8:9 (ASV)

They are all plain ...—Because the secret of the Lord is (only) with them that fear Him (Psalms 25:14), and God reveals such things to them by His Spirit (1 Corinthians 2:10), while the natural man receiveth not the things of the Spirit of God, for they are foolishness unto him (1 Corinthians 2:14; Proverbs 8:14).