Here is the reason for the good use of discipline. You were not to withhold discipline to a child. Your children were not going to die from being beat with a stick or rod. In fact, they will be saved from the underworld Sheol. If the child has a wise heart, the heart of the parents will be glad. Parents will rejoice when the lips of their children speak what is right.
We have to consider the power of God’s anger. He is due respect and fear because of his great wrath. The psalmist wanted God to teach him the number of his days so that he would have a wise heart, a heart of wisdom.