Quoted from Psa 68:19 (Sept. 67:18). 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 Luk 4:18. The captives are not the redeemed, but the enemies of Christ's kingdom, Satan, Sin, and Death. Compare on Col 2:15, and 2Co 2:14.
Gave
In the Hebrew and Septuagint, received or took; but with the sense received in order to distribute among men. Compare Gen 15:9, take for me: Gen 18:5, I will fetch for you: Exo 27:20, bring thee, i.e., take and present to thee: Act 2:33, “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 Eph 4:11 sqq.