This was a more complicated section on which to comment. Frankly, this could have been much longer if I had focused more on the questionable doctrine called the “Harrowing of Hades.” Nevertheless, I hope what I have written will be of some help or encouragement.

4:8-10 8Wherefore he saith, “When he ascended up on high, he led captivity captive, and gave gifts unto men.” 9(Now that he ascended, what is it but that he also descended first into the lower parts of the earth? 10He that descended is the same also that ascended up far above all heavens, that he might fill all things.)
v. 8: Wherefore he saith, “When he ascended up on high, he led captivity captive, and gave gifts unto men.”
Point One:
Who is the one that “saith” in verse 8? For the answer we must go to Psalm 68:18; there we find the words of David describing God as a conquering King who spoils His enemies on the mountain and then distributes the spoils as gifts to the people, including to those who are rebellious.
However, one important question that could be asked is: to what extent do we take this comparison? In other words, how specifically analogous is the story of the conquering King to the argument that Paul is making regarding the gifts and the purposes of giving them by Jesus to the Church?
Some have suggested that what is being spoken of is Christ’s ascension to the cross, while others have suggested that after descending to the “lower parts of the earth” Christ rescued those held captive in Paradise and took them “captive” to heaven.
[Note: This teaching is also called “The Harrowing of Hades” and finds support in the Apostles’ Creed: “He descended into Hades.”]
Nevertheless, it would seem the best course of action to simply keep a consistent contextual reading in mind: one that of unity within the Church and individual gifts of grace which Jesus imparts, both to His friends and those who are rebellious, to exemplify His glory and wisdom.
Point Two:
Beginning with verse seven, the context of Paul’s argument is the supplying each individual the things it needs to function properly in the Body of Christ, the Church. Are there deeper truths to be uncovered? Most certainly? However, we must not carry the analogy too far.
For as long as the author can remember, nearly every time the resurrection of Christ has been preached, the subject of Jesus descending to Paradise and taking the Old Testament saints out of there and up to heaven. The only problem is that there is nothing in the context of Ephesians 4:1-16 that addresses Paradise, hell, heaven, or even death! All that Paul addresses in these sixteen verses is the subject of unity.
Another passage that is linked to this verse is 1 Peter 3:19: “By which also he went and preached unto the spirits in prison.” But what is often never included with verse 19 is verse 20, which reads [emphasis added]: “Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water (1 Peter 3:20 KJV).
It is quite puzzling why 1 Peter 3:19 would be used as a supporting text (along with Luke 23:43, Psalm 68:18, and Ephesians 4:8-10) for a teaching claiming Jesus went to deliver the saints, when those to whom Jesus preached were the “disobedient.” It is therefore illogical to deduce from this passage in Ephesians that Paul was speaking of anything other than the unity of the Body of Christ, the power of God, the Kingship of Jesus the Conquering King, and Christ’s generosity.
v. 10b: …that he might fill all things.
Building on the image of the king that ascended to conquer his enemies, Paul speaks of Jesus’ all-encompassing Lordship with a parenthetical explanation of the logical comparison being made (beginning in verse 9). This imagery of Jesus’ omnipresent authority and power in this passage can be compared to other verses, such as: Eph 1:20-21(in the heavenly places, far above all principalities); Heb 4:14 (we have a great high priest that is passed into the heavens); Heb 7:26 (a high priest became us and made higher than the heavens).