Hebrews 5:9--"the source of eternal salvation?"

Greek (NA28): καὶ τελειωθεὶς ἐγένετο πᾶσιν τοῖς ὑπακούουσιν αὐτῷ αἴτιος σωτηρίας αἰωνίου

Robertson's WP: "Having been made perfect (τελειωθεὶς). First aorist passive participle of τελειοω, the completion of the process of training mentioned by this same verb in Hebrews 2:10 'by means of sufferings' (διὰ παθημάτων) as stated again here in verse Hebrews 5:8."

NET Bible: "And by being perfected in this way, he became the source of eternal salvation to all who obey him"

In what sense was Christ perfected? The LXX uses the language of perfecting, accomplishing or consecrating within a priestly context. See Exodus 29:9, 29, 33, 35; Leviticus 4:5; 8:33; 21:10; Numbers 3:3. Compare Hebrews 7:28. It seems that Jesus was made perfect for the position of high priest through suffering and obedience even to death.

ἐγένετο πᾶσιν τοῖς ὑπακούουσιν αὐτῷ-This passage makes an interesting comparison between Jesus, who learned obedience (ἔμαθεν ἀφ' ὧν ἔπαθεν τὴν ὑπακοήν) from the things which he suffered, and all those who obey Christ and benefit from such obedience (cf. Hebrews 2:10; 11:8). The noun phrase is dative plural masculine: ὑπακούουσιν is the present active participle dative plural masculine of ὑπακούω.

BDAG: αἴτιος, ία, ον ⟦aítios⟧ (Hom.+) 1 pert. to being the cause of someth., in our lit. only subst. A ὁ αἴ. one who is the cause, source αἴ. σωτηρίας Hb 5:9 (Hdt. et al.; Diod S 4, 82 αἴ. ἐγένετο τῆς σωτηρίας; SIG 1109, 80; Philo, Agr. 96, Spec. Leg. 1, 252 θεὸν τ. σωτηρίας αἴτιον al.; Jos., Ant. 14, 136; Bel 42; 2 Macc 4:47; 13:4; EpArist 205; Just., D. 3, 5; 4, 1; Tat., Ath.). B neut. cause, reason (Hdt., Thu. et al.; PHib 73, 18 [243/242 b.c.]; BGU 1121, 27; 29; Philo; Jos., Ant. 7, 75; 12, 84; Just., D. 5, 6; Tat.; Ath. 19, 2) μηδενὸς αἰ. ὑπάρχοντος i.e. the crowd will be unable to explain its action Ac 19:40. 2 ground for legal action. τὸ αἴτ.= αἰτία 3a in a legal expr. ground for complaint, basis for a charge αἴ. εὑρίσκειν ἔν τινι Lk 23:4, 14. οὐδὲν αἴ. θανάτου no ground for capital punishment vs. 22.—DELG. M-M. Sv.

As one can see above, BDAG favors "cause, "source" as a meaning for αἴτιος in Hebrews 5:9. For classical denotations of this word, see LSJ. Paul Ellingworth discusses LXX and classical uses of αἴτιος in The Epistle to the Hebrews. See 1 Samuel 22:22; Aristotle, Physics 194b30; Polyb. 1.43.2; Philo, Spec. Leg. 1.252; Josephus Ant. 14.8.2 § 136. The Greek word appears once in the GNT, in Heb. 5:9. See Harold W. Attridge, Hebrews: A Commentary, page 154; Louw-Nida, Semantic Domain 89.15.

Abbott-Smith on αἴτιος : causative of, responsible for; as subst., ὁ αἰ., the cause, author: He 5:9; τὸ αἰ., the cause, Ac 19:40.

σωτηρίας αἰωνίου-Westcott points to Isaiah 45:17 in the LXX. Compare Hebrews 9:12, 15.