A.T. Robertson Commentary Hebrews 11:4

"By faith Abel offered unto God a more excellent sacrifice than Cain, through which he had witness borne to him that he was righteous, God bearing witness in respect of his gifts: and through it he being dead yet speaketh." — Hebrews 11:4 (ASV)

A more excellent sacrifice (πλειονα θυσιαν). Literally, "more sacrifice" (comparative of πολυς, much). For this rather free use of πλειων with the point implied rather than stated see Mt 6:25; Luke 10:31; 12:23; Hebrews 3:3.

Than Cain (παρα Καιν). For this use of παρα after comparative see 1:4,9. For the incident see Ge 4:4.

Through which (δι' ης). The sacrifice (θυσια).

He had Witness borne to him (εμαρτυρηθη). First aorist passive indicative of μαρτυρεω as in verse 2, "he was witnessed to."

That he was righteous (εινα δικαιος). Infinitive in indirect discourse after εμαρτυρηθη, personal construction of δικαιος (predicate nominative after εινα) agreeing with the subject of εμαρτυρηθη (cf. Romans 1:22, εινα σοφο).

God bearing witness (μαρτυρουντος του θεου). Genitive absolute with present active participle of μαρτυρεω.

Through it (δι' αυτης). Through his faith (as shown by his sacrifice). Precisely why Abel's sacrifice was better than that of Cain apart from his faith is not shown.

Being dead (αποθανων). Second aorist active participle of αποθνησκω, "having died."

Yet speaketh (ετ λαλε). Cf. Genesis 4:10; Hebrews 12:24. Speaks still through his faith.