The writer reasons from the lesser to the greater. His readers had fathers who corrected them, and they still "gave them reverence." Barnes describes that respect: "We submitted to them; honored them; loved them." If they honored earthly fathers, how much more should they yield to God? The title "Father of spirits" sets God apart from "fathers of our flesh." Barnes compares Numbers 16:22, where God is called "the God of the spirits of all flesh," and Gill explains that He is so called as the Creator of the souls of men. The last two words, "and live," hold out a promise: submission to God leads to life.

The writer answers by showing how God's correction differs from that of earthly fathers: "For they verily for a few days chastened us after their own pleasure; but he for our profit, that we might be partakers of his holiness" (Hebrews 12:10). He admits the cost and names the fruit: "no chastening for the present seemeth to be joyous, but grievous: nevertheless afterward it yieldeth the peaceable fruit of righteousness unto them which are exercised thereby" (Hebrews 12:11). Then he calls them to act: "lift up the hands which hang down" (Hebrews 12:12).

"Fathers of our flesh" means earthly fathers, the ones Barnes calls "those from whom we have derived our being here." The phrase "Father of spirits" echoes the prayer of Moses and Aaron in Numbers 16:22, "O God, the God of the spirits of all flesh," which Barnes cites. Barnes suggests the name is given to God because the soul is the most important part of a person. On "and live," Barnes explains that God's "fatherly chastisements are adapted to secure our spiritual life." Gill takes it to mean living more comfortably and more to God's glory in fellowship with Him now, and in heaven forever.

This question shows God as a better Father than the best earthly one. Earthly fathers corrected "for a few days" and "after their own pleasure," sometimes getting it wrong. God corrects "for our profit" with one aim: "that we might be partakers of his holiness" (Hebrews 12:10). Matthew Henry's Concise Commentary sums it up: "God's correction is not condemnation."

The promise tucked into the question matters too. Yielding to God is not loss; it is the way to life. The writer pictures God's training producing "the peaceable fruit of righteousness" (Hebrews 12:11).