This verse has been controversial, but is nonetheless very important. The context is taken from Psalm 68:17-20: "The chariots of God are twenty thousand, even thousands of angels: . . . Thou hast ascended on high, thou hast led captivity captive: . . . our God is the God of salvation; and unto God the Lord belong the issues from death."

The psalmist is apparently describing the Lord among His heavenly hosts, riding home as a mighty king returning with the spoils of battle. Evidently this prize of battle consisted of His own people who had been held captive in an alien land, but who now in turn had been captured from the enemy by the returning King. To do this, the King (none other than the Lord Jesus Himself) "ascended up on high," leading them to His own throne in the heavens.

But first He had to descend to the earth, and then even to "the lower parts of the earth." This unusual phrase must refer to the great pit in the center of the earth confining the souls of the dead--the place called Hades.

One of Christ’s purposes on earth was "to proclaim liberty to the captives, and the opening of the prison to them that are bound" (Isaiah 61:1). That is exactly what He did when He died on the cross for the sins of these very captives, then, in the Spirit, descended into Hades to set them free.

He returned with the very "keys of hell and of death" (Revelation 1:18), alive forevermore. The souls of those who had died in faith came with Him, finally ascending with Him into "paradise," in "the third heaven" (note Luke 23:43; 2 Corinthians 12:2, 4) to wait with Him for His future return to reclaim the whole earth. HMM

http://www.icr.org/article/6334/