Vincent's NT Word Studies
8. Wherefore. Confirming by Scripture what has just been said.When He ascended, etc. Quoted from Psalm lxviii. 19 (Sept. lxvii. 18). The Hebrew reads: "Ascending to the height thou didst lead captive captivity, and received gifts in man." So Sept. Paul changes thou didst lead, didst receive, into he lead and he gave. The Psalm is Messianic, a hymn of victory in which God is praised for victory and deliverance. It is freely adapted by Paul, who regards its substance rather than its letter, and uses it as an expression of the divine triumph as fulfilled in Christ's victory over death and sin.
Ascended. The ascent of Jehovah is realized in Christ's ascent into heaven.
Captivity. Abstract for the body of captives. See on Luke iv. 18. The captives are not the redeemed, but the enemies of Christ's kingdom, Satan, Sin, and Death. Compare on Col. ii. 15, and 2 Cor. ii. 14. Gave. In the Hebrew and Septuagint, received or took; but with the sense received in order to distribute among men. Compare Gen. xv. 9, take for me: xviii. 5, I will fetch for you: Exod. xxvii. 20, bring thee, i.e., take and present to thee: Acts ii. 33, "Having received of the Father, etc., He hath shed forth." Thus Paul interprets the received of the Old Testament. His point is the distribution of grace by Christ in varied measure to individuals. He confirms this by Scripture, seeing in the Jehovah of this Old-Testament passage the Christ of the New Testament - one Redeemer under both covenants - and applying the Psalmist's address to Christ who distributes the results of His victory among His loyal subjects. These results are enumerated in ver. 11 sqq.
Robertson's NT Word Studies
4:8 {Wherefore he saith} (dio legei). As a confirmation of what Paul has said. No subject is expressed in the Greek and commentators argue whether it should be ho qeos (God) or he grafe (Scripture). But it comes to God after all. See #Ac 2:17. The quotation is from #Ps 68:18, a Messianic Psalm of victory which Paul adapts and interprets for Christ's triumph over death. {He led captivity captive} (eicmalwteusen aicmalwsian). Cognate accusative of aicmalwsian, late word, in N.T. only here and #Re 13:10. The verb also (aicmalwteuw) is from the old word aicmalwtos, captive in war (in N.T. only in #Lu 4:18), in LXX and only here in N.T.