Jamieson, Fausset and Brown on Hebrews 12:8

8. 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 (He 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].