Prov 18:4

“"The word in the heart of man is a deep water, and a river and fountain of life spring forth." By "deep water" he [Solomon] means "abundant" water which can often produce many rivers instead of one. Or, he says: it contains it deeply hidden in itself. As water is immeasurable, so the word in the heart of the person who lives according to God is without limit. Therefore, he uses "word" for knowledge. This is the one in whose heart a fountain of water is made when he hears the words of Jesus. He [Solomon] then speaks of it "springing forth," raining upon or watering the fields which makes them fertile.”

“Deep water, the words from the mouth of a man, etc. The words of the wise are compared to water because they both wash the minds of the listeners and irrigate them, lest they remain deformed by the filth of sins, or waste away through lack of heavenly doctrine, and as if perish through harmful dryness. And because in these same words of teachers, certain mystical and hidden things lie, which are comprehended by more diligent effort, while certain other things flow openly and easily to be understood by all who listen; rightly do they call these both deep water and an overflowing torrent. But it can also be distinguished in this way, that because the Scripture of the Old Testament is given typically, it is said of it, Deep water, words from the mouth of a man, because the Lord and the apostles openly revealed the mysteries of both Testaments to the world, it is added concerning them, And an overflowing torrent, a fountain of wisdom.”