Lift up your heads, O ye gates; and be ye lift up, ye everlasting doors; and the King of glory shall come in.
As the ark in the procession draws near the gates of Zion, David calls on them to open to receive the King of Glory.
Lift up your heads, O ye gates - i:e., Be elated with the high honour which you have, in the entrance through you of God's own ark. Not, as Grotius thinks, alluding to a kind of portcullis [katarraktai] which is opened by being lifted up; because the expression is, Lift up your heads, which is evidently a poetical personification. The ark was accompanied with the presence of Yahweh Himself. Its settlement marked a new era in God's relations to His people (1 Samuel 6:1; 1 Samuel 6:21; 2 Samuel 6:2). His presence, symbolized by the ark, ensures their safety (Numbers 10:35-36).