earth is the Lord's. Every part of the planet belongs to God by right of creation, and it is His prerogative to give each portion of it to any nation He chooses, and only for as long as He chooses (note Acts 17:24-26).

upon the seas. Initially the created earth was all water, but on the third day of creation week, God “laid the foundations of the earth” (Job 38:4), and it was founded “above” (a better translation of the Hebrew word in this context than “upon”) the seas and the great rivers (“the floods”).

Who shall ascend. In context, this seems to be a prophecy of the ascension of Christ back to heaven after His death and resurrection.

ye everlasting doors. The entrance of the Savior into the heavenly city through its pearly gates and everlasting doors is acknowledged twice (Psalm 24:7, 9), perhaps referring to two different ascensions and entrances. The first would surely be after His defeat of Satan at the cross (“mighty in battle”), when He brought the Old Testament saints with Him from Hades to the heavenly Paradise (see note on Ephesians 4:9). The second could then well be at the rapture of the church (1 Thessalonians 4:13-17).

Who is this. It is clearly a righteous Man (Psalm 24:4) who ascends to the hill of the Lord and for whom the “everlasting doors” are lifted up (Psalm 24:9). Yet this glorious King is also the Lord of hosts. This could only be true of the ascending God/Man, Jesus Christ.