John Calvin Commentary Hebrews 12:10

"For they indeed for a few days chastened [us] as seemed good to them; but he for [our] profit, that [we] may be partakers of his holiness." — Hebrews 12:10 (ASV)

For they verily for a few days, etc. The second amplification of the subject, as I have said, is that God’s chastisements are appointed to subdue and mortify our flesh, so that we may be renewed for a heavenly life. From this it appears that the fruit or benefit is to be perpetual; but such a benefit cannot be expected from humans, since their discipline refers to civil life and therefore properly belongs to the present world. It therefore follows that these chastisements bring far greater benefit, as the spiritual holiness conferred by God far exceeds the advantages that belong to the body.

If anyone were to object and say that it is the duty of parents to instruct their children in the fear and worship of God, and that therefore their discipline seems not to be confined to so short a time, the answer to this is that this is indeed true. However, the Apostle speaks here of domestic life, as we commonly speak of civil government. For although it belongs to magistrates to defend religion, we say that their office is confined to the limits of this life, because otherwise the civil and earthly government cannot be distinguished from the spiritual kingdom of Christ.

Moreover, when God’s chastisements are said to be profitable to make people partners of his holiness, this is not to be understood as though they make us really holy, but that they are helps to sanctify us, for by them the Lord exercises us in the work of mortifying the flesh.