But if you are without chastening, of which all have become partakers, then you are illegitimate and not sons.
Verse 8 is the reverse of verse 7.
But if you are without chastening,
“Chastening” involves severe discipline from God. The word means child-training. The idea is “discipline” or “education.” If God excludes a person entirely from chastening, then that is an indication that that person is not a believer.
of which all have become partakers [companions, sharers],
“All” here are true believers, true “sons” of God. God’s discipline is something He does with believers, not unbelievers.
then you are illegitimate and not sons.
Those not subject to divine discipline are not legitimate believers. They are illegitimate fakers. The word “illegitimate” carries a legal idea. These are people who have not had the privileges of the family of God because they are not believers.
However, this verse does not say that the readers of Hebrews are not Christians because he has already made the point that they are true believers (He 12:5–7).
Those without divine discipline are not Christians.
No Christian should be surprised by divine discipline. It is part of being a member of the family of God. Any other concept of divine discipline is off base.
Divine discipline is an indication of sonship. Absence of this in one’s life is evidence that there is no genuine relationship with God. Genuine sonship makes divine discipline necessary.
How does one know if they are illegitimate? is it because they are non believer?
Lana, yes, they are illegitimate because they are unbelievers. God does not discipline non-Christians because they cannot grown in Christ. They are dead to Christ.
How does one know if they are being chastened? How does God chasten his children, and what form does it take?
Tom, God customizes discipline according to each individual. There is no specific answer to your question. I encourage you to read all of the studies leading up to this verse and away from this verse.