John Gill Commentary Psalms 24:9

"Lift up your heads, O ye gates; Yea, lift them up, ye everlasting doors: And the King of glory will come in." — Psalms 24:9 (ASV)

Lift up your heads, O you gates even lift [them] up, you
everlasting doors; and the King of glory shall come in .
(See Gill on Psalms 24:7). This is repeated on account of the backwardness and negligence of churches, and particular believers, to open and let Christ in; as may be seen in the case of the church in (Song of Solomon 5:2Song of Solomon 5:3) ; as well as the more to set forth the greatness and glory of Christ, about to make his entrance, and to command a proper awe and reverence of him: some think respect is had to the twofold coming of Christ; first into the second temple, and next at the last judgment; though rather the certainty of his coming, in a spiritual manner, to his church and people, is here designed.