"Ascended on high" means he went up to heaven. "Descended into the lower parts of the earth" means he came down from heaven to the earth. The "lower parts of the earth," in Psalm 139:15, refers to David.
Psa 139:15 My substance was not hid from thee, when I was made in secret, and curiously wrought in the lowest parts of the earth.
Either "lowest parts of the earth" refers to David's mother's womb or it refers to the
surface of the earth where David's mother was when she conceived him.
The "Scriptural order" has him descending from heaven first.
He also first descended into the lower parts of the earth.
Before He ascended into heaven,
He first descended into the lower parts of the earth.
That is what the scripture says in black and white.
(Now this, "He ascended"--what does it mean but that
He also first descended into the lower parts of the earth?
That is the scriptural order.
These verses are a reference
to what happened after the cross, and the resurrection of Jesus Christ.
8 Therefore He says: "When He ascended on high, He led captivity captive, And gave gifts to men."
9 (Now this, "He ascended"--what does it mean but that
He also first descended into the lower parts of the earth?
10 He who descended is also the One who ascended far above all the heavens, that He might fill all things.)
11 And He Himself gave some to be apostles, some prophets, some evangelists, and some pastors and teachers,
12 for the equipping of the saints for the work of ministry, for the edifying of the body of Christ,
13 till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ;
14 that we should no longer be children, tossed to and fro and carried about with every wind of doctrine, by the trickery of men, in the cunning craftiness of deceitful plotting,
15 but, speaking the truth in love, may grow up in all things into Him who is the head--Christ--
16 from whom the whole body, joined and knit together by what every joint supplies, according to the effective working by which every part does its share, causes growth of the body for the edifying of itself in love.
Ephesians 4:8-16
He first descended...
as it is written -
For as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights
in the heart of the earth. Matthew 12:40
The Lord descended down into the heart of the earth for three days and three nights after He was crucified on the cross.
JLB