The readers were growing weary under hardship, and they had lost hold of what Scripture says about it. The KJV words this as a statement, "And ye have forgotten the exhortation." Barnes says the verse "might be rendered as a question," which he thinks fits the writer's purpose better, and Gill allows the same reading: "it may be read by way of question." Either way, the writer is calling them back to Proverbs 3:11-12. Gill calls this exhortation a "consolation," a word of comfort. Barnes says Solomon may have been addressing a son literally, or all the godly as a father to them, or the words may be God Himself addressing His children, and that whichever view is taken the sense is the same, so it speaks to these readers too.

The writer answers by quoting the words they had forgotten: "My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him: For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth" (Hebrews 12:5-6). He then explains them: God deals with them "as with sons" (Hebrews 12:7), and His chastening is "for our profit, that we might be partakers of his holiness" (Hebrews 12:10). He closes the thought with a call to action: "Wherefore lift up the hands which hang down, and the feeble knees" (Hebrews 12:12).

The words come from Proverbs 3:11-12: "My son, despise not the chastening of the LORD; neither be weary of his correction: For whom the LORD loveth he correcteth; even as a father the son in whom he delighteth." Gill names this source.

The word "chastening" is the Greek paideia, which Thayer's lexicon defines as "the whole training and education of children." Barnes says it does not mean every hardship, but "that kind of affliction which is designed to correct us for our faults." The exhortation warns against two opposite mistakes. "Despise not" (oligoreo, to regard lightly) means, in Barnes' words, do not treat it "as a small matter." "Nor faint" (ekluo, to give out or lose heart) means do not collapse under it.

The first thing the writer wants them to remember is how Scripture addresses them: "as unto children." Before it says anything about chastening, it says "My son." Matthew Henry's Concise Commentary puts it this way: "God may let others alone in their sins, but he will correct sin in his own children." Hardship under God's hand is not a sign that He has walked away.

The exhortation also guards against two opposite errors. Barnes says believers are first to consider the purpose of God's correction and then "to bear up under them, however severe they may be." One person shrugs off what God is teaching; another is crushed by it. God's word steers between both, toward a child's trust in a loving Father.