Jamieson, Fausset and Brown on Hebrews 12:5

5. forgotten--"utterly," so the Greek. Compare He 12:15-17, in which he implies how utterly some of them had forgotten God's word. His exhortation ought to have more effect on you than the cheers and exhortations of the spectators have on the competitors striving in the games.

which--Greek, "the which," of which the following is a specimen [Alford].

speaketh unto you--as in a dialogue or discourse, so the Greek, implying God's loving condescension (compare Is 1:18).

despise not--literally, "Do not hold of little account." Betraying a contumacious spirit of unbelief (He 3:12), as "faint" implies a broken-down, weak, and desponding spirit. "Chastening" is to be borne with "subjection" (He 12:9); "rebuke" (more severe than chastening) is to be borne with endurance (He 12:7). "Some in adversity kick against God's will, others despond; neither is to be done by the Christian, who is peculiarly the child of God. To him such adverse things occur only by the decree of God, and that designed in kindness, namely, to remove the defilements adhering to the believer, and to exercise his patience" [Grotius].