Jamieson, Fausset and Brown on Hebrews 12:9

9. fathers ... which corrected us--rather as Greek, "We had the fathers of our flesh as correctors."

subjection--See the punishment of insubordination, De 21:18.

Father of spirits--contrasted with "the fathers of our flesh." "Generation by men is carnal, by God is spiritual" [Bengel]. As "Father of spirits," He is both the Originator, and the Providential and Gracious Sustainer, at once of animal and spiritual life. Compare "and LIVE," namely, spiritually; also He 12:10, "that we might be partakers of His holiness" (2Pe 1:4). God is a spirit Himself, and the Creator of spirits like Himself, in contrast to men who are flesh, and the progenitors of flesh (Joh 3:6). Jesus our pattern "learned obedience" experimentally by suffering (He 5:8).

and live--and so, thereby live spiritually and eternally.