John Gill Commentary Proverbs 18:4

"The words of a man`s mouth are [as] deep waters; The wellspring of wisdom is [as] a flowing brook." — Proverbs 18:4 (ASV)

The words of a man's mouth [are as] deep waters
The words of a great and mighty man; of an excellent and valuable man, as Jarchi; or of a wise man, as Aben Ezra. The doctrines which such a man has imbibed, and his heart is full of and his mouth utters, are like to "waters", pure, purifying, and refreshing; to "deep waters", which make no noise, and cannot be easily fathomed: such are the deep mysteries of grace, the wisdom of God in a mystery, spoken among them that are perfect; of which a good man makes no boast, but humbly declares; out of the abundance of his heart, his mouth speaks;

[and] the wellspring of wisdom [as] a flowing brook ;
there is a spring of spiritual wisdom and knowledge in him; a well of living water, springing up unto everlasting life; and from thence it flows freely and constantly; communicating itself liberally unto others, and ministering grace to the hearers, for their edification.