Today's Proverbs change authors. Instead of Solomon, we are hearing from a guy named Agur. He was speaking these proverbs to Ithiel and Ucal. Nothing else is known about them (according to the footnotes in my fancy study Bible) But the ones who compiled the book of Proverbs obviously found the words of Agur to be on par with those of Solomon since they are included.
5 Every word of God is pure; He is a shield to those who take refuge in Him. 6 Don't add to His words, or He will rebuke you, and you will be proved a liar. Holman Christian Standard
The New American Standard Bible (NASB) translates v. 5 this way "Every word of God is tested"The NIV says, "flawless."
I think that has the same meaning when you think of pure metals and how they are tested with fire and made pure.
Either way, Agur is reminding us that we can totally trust in God's word because it is pure, tested, flawless.
There has been a consistent attack on the Word of God over the past 30-40 years. Many who want to justify their personal sins will say something like "Well. That just applied to people of the time when the Bible was written. Times have changed. Paul wouldn't say that now."
These people should heed the warning found in v.6 "Don't add to His words, or He will rebuke you, and you will be proved a liar."
The Apostle John in Revelation gave this warning.
22:18 I testify to everyone who hears the prophetic words of this book: If anyone adds to them, God will add to him the plagues that are written in this book. 19 And if anyone takes away from the words of this prophetic book, God will take away his share of the tree of life and the holy city, written in this book.
God is serious about His Word. We should be too.