The man that wandereth out of the way of understanding.

Proverbs 21:16 "The man that wandereth out of the way of understanding shall remain in the congregation of the dead"

This is a Spiritual understanding, understanding the Words of God that Jesus taught us. Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock. The rain came down, the streams rose, and the winds blew and beat against that house; yet it did not fall, because it had its foundation on the rock. (Mateo 7:24-25)

Our solid foundation is understanding the Words of God which is the rock of our salvation, what the Lord say if we didn't practice it.

But everyone who hears these words of mine and does not put them into practice is like a foolish man who built his house on sand. The rain came down, the streams rose, and the winds blew and beat against that house, and it fell with a great crash. (Mateo 7:26-27)

If we understand the Words of God, we will follow Him but If not and we live out of the way of His understanding we are like a fools and remain in the congregation of the dead, dead in faith.

Here is king Solomon Advice, "My son, if you accept my words and store up my commands within you, turning your ear to wisdom and applying your heart to understanding, and if you call out for insight and cry aloud for understanding, and if you look for it as for silver and search for it as for hidden treasure, then you will understand the fear of the Lord and find the knowledge of God". (Proverbs 2:1-5)