Albert Barnes Commentary Hebrews 12:8

"But if ye are without chastening, whereof all have been made partakers, then are ye bastards, and not sons." — Hebrews 12:8 (ASV)

But if you are without chastisement. If you never meet with anything that is adapted to correct your faults, to subdue your temper, to chide your wanderings, it would prove that you were in the condition of illegitimate children—cast off and disregarded by their father.

Of which all are partakers. All who are the true children of God.

Then you are bastards, and not sons. The reference here is to the neglect with which such children are treated, and to the general lack of care and discipline over them:

"Lost in the world's wide range; enjoined no aim,
Prescribed no duty, and assigned no name." Savage.

In the English law, a bastard is termed nullius filius. Illegitimate children are usually abandoned by their father. The care of them is left to the mother, and the father endeavors to avoid all responsibility, and usually to be concealed and unknown. His own child he does not wish to recognize; he neither provides for him, nor instructs him, nor governs him, nor disciplines him.

A father who is worthy of the name, will do all these things. So Paul says it is with Christians. God has not cast them off. In every way he shows towards them the character of a father.

And if they passed along through life without any occurrence that would indicate the paternal care and attention designed to correct their faults, it would show that they never had been his children, but were cast off and wholly disregarded. This is a beautiful argument; and we should receive every affliction as full proof that we are not forgotten by the High and Holy One who condescends to sustain the character, and to show towards us, in our wanderings, the watchful care of a Father.