Eph 4:9 and Eph 4:10 are parenthetical, showing what the ascension of Christ presupposes. By descending into the depths and ascending above all, He entered upon His function of filling the whole universe, in virtue of which function He distributes gifts to men. See Eph 1:23. Rev., properly, inserts this, thus giving the force of the article which calls attention to the fact of ascension alluded to in the quotation. “Now the or this 'He ascended.”'
What is it but
What does it imply?
Descended first (καὶ κατέβη)
His ascent implies a previous descent. A.V. reads first, following the Tex. Rec. πρῶτον. Rev., correctly, He also descended. Compare Joh 3:13.
The lower parts of the earth (τὰ κατώτερα μέρη τῆς γῆς)
The under world. The reference is to Christ's descent into Hades. Some give the words a comparative force, deeper than the earth.