John Chrysostom

Then again he argues from the general custom. Seest thou how he brings up arguments from all quarters, from facts in the Scripture, from its words, from our own notions, from examples in ordinary life? "But if ye be without chastisement" and so on. Seest thou that he said what I just mentioned, that it is not possible to be a son without being chastened? …

Homily on Hebrews 29 ↗

Oecumenius

"If you are not disciplined." Where he had sought from the things themselves, namely with all the saints brought forth who had fought through afflictions, now he strives to persuade even from human reasoning. "then you are not legitimate, not true sons and daughters at all." If, therefore, the sign of illegitimate children is not to be punished, but legitimate children are punished, it is necessary, he says, to rejoice in punishment.

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

677. – Then (v. 8) he argues from what he has already said: first, he concludes to something unwelcome; secondly, by giving an example (v. 9); thirdly, he mentions the resulting usefulness (v. 11). 678. – In regard to the first he gives this reason: All the saints who have pleased God passed through many tribulations, by which they were made sons of God. Therefore, one who does not persevere in discipline is not a son but a bastard, i.e., born of adultery. …

Commentary on Hebrews ↗