A book of the Bible doesn’t have to have a verse or verses that announce the theme. But, if Proverbs has one, usually people appeal to at least the first two verses in this passage in chapter 3:
Trust in the LORD with all your heart,
Proverbs 3:5–8; ESV
and do not lean on your own understanding.
In all your ways acknowledge him,
and he will make straight your paths.
Be not wise in your own eyes;
fear the LORD, and turn away from evil.
It will be healing to your flesh
and refreshment to your bones.
I’ve seen this passage quoted often. It obviously summarizes a great deal of what the whole Bible says about Christian living and Christian attitudes.
But it doesn’t say much that is unique to Proverbs.
The importance of wisdom, and the importance of receiving God’s Word in order to posses wisdom, isn’t unique to Proverbs. Deuteronomy arguably covers the same ground. So do some of Paul’s letters.
If Proverbs has a theme verse, it should relate to what is unique about Proverbs.
I nominate this passage in which Wisdom personified describes herself:
By me kings reign,
Proverbs 8:15–16; ESV
and rulers decree what is just;
by me princes rule,
and nobles, all who govern justly.
When I first started studying and memorizing Proverbs, this text helped me figure out a recurring topic in Proverbs that was addressed in many ways once one learned to recognize it. Solomon is a king addressing “my son” or “my sons.” It is thus addressed to someone who is to inherit authority.
Proverbs is about young men becoming “kings” rather than slaves. I argue for this and build on it extensively in my forthcoming book on Proverbs. It will probably also be the subject of future blog posts here.