Verse 19. As many as I love, I rebuke and chasten. Of course, only on the supposition that they deserve it. The meaning is, that it is a proof of love on his part, if his professed friends go astray, to recall them by admonitions and by trials. So a father calls back his children who are disobedient; and there is no higher proof of his love than when, with great pain to himself, he administers such chastisement as shall save his child. See the sentiment here expressed fully explained. See Barnes "Heb 12:6, seq. The language is taken from Pr 3:12

Be zealous therefore, and repent. Be earnest, strenuous, ardent in your purpose to exercise true repentance, and to turn from the error of your ways. Lose no time; spare no labour, that you may obtain such a state of mind that it shall not be necessary to bring upon you the severe discipline which always comes on those who continue lukewarm in religion. The truth taught here is, that when the professed followers of Christ have become lukewarm in his service, they should lose no time in returning to him, and seeking his favour again. As sure as he has any true love for them, if this is not done, he will bring upon them some heavy calamity, alike to rebuke them for their errors, and to recover them to himself.

{c} "As many" Heb 12:5,6