But if ye be 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.
Whereof all are partakers - All who are the true children of God.
Then are ye bastards, and not sons - The reference here is to the neglect with which such children are treated, and to the general want of care and discipline over them:
"Lost in the world's wide range; enjoin'd no aim,
Prescrib'd no duty, and assign'd 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 evinces toward them the character of a father. And if it should be that 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 to us the character, and to evince toward us, in our wanderings, the watchful care of a Father.

Then are ye bastards - This proceeds on the general fact, that bastards are neglected in their manners and education; the fathers of such, feeling little affection for, or obligation to regard, their spurious issue. But all that are legitimate children are partakers of chastisement or discipline; for the original word παιδεια does not imply stripes and punishments, but the whole discipline of a child, both at home and at school.

But if ye be without chastisement,.... Or have no affliction:
whereof all are partakers; that is, all the children of God; they are all alike children; they are all in a state of imperfection, and prone to sin; God has an impartial respect unto them: and though they are not all alike chastened, nor chastened at all times, yet none are exempted from chastisement, but have it in some way or another, and at some time or another.
Then are ye bastards, and not sons; all are not sons that are under a profession of religion; all that are under a profession of religion are not chastised; but then those are not the children of God, but the children of the world, of Satan, and of the antichristian harlot; for though all that are chastised are not children, yet all that are children are chastised: hence we learn, that outward peace and prosperity is not a note of a true church; and that such have reason to distrust their state, who know not what it is to have the chastising rod of God upon them; and that afflictions are rather arguments for than against sonship.

if ye be without--excluded from participation in chastisement, and wishing to be so.
all--all sons: all the worthies enumerated in the eleventh chapter: all the witnesses (Hebrews 12:1).
are--Greek, "have been made."
then are ye bastards--of whom their fathers take no care whether they are educated or not; whereas every right-minded father is concerned for the moral well-being of his legitimate son. "Since then not to be chastised is a mark of bastardy, we ought [not to refuse, but] rejoice in chastisement, as a mark of our genuine sonship" [CHRYSOSTOM].

Of which all sons are partakers - More or less.