What does Proverbs 18:2 mean?

The book of Proverbs contrasts foolishness with godly wisdom. True wisdom is rooted in pursuit of God and His truth (Proverbs 1:7). The prior proverb noted that those who "isolate" from sound judgment are trying to ignore anything not in line with their preferences. There's an arrogance behind someone who separates themselves from all other opinions, as if no one else can contribute to his understanding.

A "fool" isn't driven by a desire to understand; all that matters to the fool is saying what's on their mind. One might say such a person has a closed mind and an open mouth. Discussions become bitter arguments when we fail to listen with the intent of understanding. A foolish approach is to listen only so one knows when they can start talking.

Many Pharisees in Jesus' day refused to learn from Him. While others were astonished at Jesus' teaching, the Pharisees smugly thought they knew all about the Old Testament. However, Jesus rebuked them by saying, "His [the Father's] voice you have never heard, his form you have never seen, and you do not have his word abiding in you, for you do not believe the one whom he has sent. You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about me, yet you refuse to come to me that you may have life" (John 5:37–40).