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.'

This contrast confirms the contrast in Hebrews 12:9. If we remember back to the earthly chastening of our parents we will remember that it was only temporary, ‘for a few days'. And while they chastened us in the way that they thought best, they may well sometimes have been wrong. But with our heavenly Father we can be sure that any chastening is solely for our benefit, is appropriate, will strengthen our spirits and will last no longer than is necessary. He is never wrong. And His watch over us is total for He is the Father of our spirits, and of all the spirits of those who are righteous through faith.

And His purpose in it is that we might become holy in our spirits as He is. For He longs for us, and determines for us, that we may partake in His holiness, receiving it, enjoying it and being filled with it deep within, that we may be strengthened with power by His Spirit in the inner man, resulting in the indwelling of Christ, and our being rooted and grounded in love, so that we may know the love of Christ which passes all knowledge and be filled ‘unto all the fullness of God' (Ephesians 3:16). That then is why He chastens us, to make us like Himself in His perfect holiness.

And what is the holiness of God? It is that which sets God apart from men, that which distinguishes Him as ‘different'. He is set apart in His perfect purity and truth, in His absolute righteousness and true goodness. So are we to be transformed into His likeness.

‘For a few days.' This may mean that chastening never lasted long, but was only temporary, or it may refer to the period of childhood as being relatively only ‘for a few days'. Either way the stress is on the temporary nature of chastisement, both men and God's. It will not last for ever.

Of course this is not the only explanation for having to endure ‘chastisement'. The Book of Job gives another, and the sufferings of Jesus were not because of any lack in Him, although He learned from them and through them was made perfect for the task He had to do (Hebrews 2:10), while the blood of the Martyrs became the seed of the church, they were a divine advertisement. But these were the exceptions rather than the rule. But all benefited by it in one way or another and in general the principle applies. God's chastisement is with our holiness in view.