(Proverbs 17:16 KJV) Wherefore is there a price in the hand of a fool to get wisdom, seeing he hath no heart to it?
Even a “fool” (3684) has the “price” (4242) required to understand the plan of God. That would seem to me to be one way to read this. It goes along with the idea that Jesus died for all and everyone can be saved. One of the features of the Bible and the gospel is that children can grasp the basics while erudite scholars can still search the depths. At both levels you can have the “price” and know the living God.
One of the problems of the fool is that he rejects the truth given to him and insists on staying in his sin. Modern man glories in rejecting the idea of sin, let alone that he is a sinner. As the saying goes, why would you need a savior when you are not lost?
So? When you rub up against, or run head-long into, the person who does not seem to understand the need for Jesus relax and let the Holy Spirit do the convicting. The problem is usually not knowledge or understanding. It is a foolish heart.