Lift up your heads, O ye gates - Either the gates of the city, or of the house erected for the worship of God; most probably, as has been remarked, the former. This may be supposed to have been uttered as the procession approached the city where the ark was to abide, as a summons to admit the King of glory to a permanent residence there. It would seem not improbable that the gates of the city were originally made in the form of a portcullis, as the gates of the old castles in the feudal ages were, not to “open,” but to be “lifted up” by weights and pullies. In some of the old ruins of castles in Palestine there are still to be seen deep grooves in the “posts” of the gateway, showing that the door did not open and shut, but that it was drawn up or let down. (The Land and the Book, vol. i. p. 376. One such I saw at Carisbrooke Castle on the Isle of Wight; and they were common in the castles erected in the Middle Ages.) There were some advantages in this, as they could be suddenly “let down” on an enemy about to enter, when it would be difficult to close them if they were made to open as doors and gates are commonly made. Thus understood, the “heads” of the gates would be the top, perhaps ornamented in some such way as to suggest the idea of a “head,” and the command was that these should be elevated to admit the ark of God to pass.
And be ye lift up, ye everlasting doors - The doors of a city or sanctuary that was now to be the permanent place of the worship of God. The ark was to be fixed and settled there. It was no longer to be moved from place to place. It had found a final home. The idea in the word “everlasting” is that of permanence. The place where the ark was to abide was to be the enduring place of worship; or was to endure as long as the worship of God in that form should continue. There is no evidence that the author of the psalm supposed that those doors would be literally eternal, but the language is such as we use when we say of anything that it is permanent and abiding.
And the King of glory shall come in - The glorious King. The allusion is to God as a King. On the cover of the ark, or the mercy-seat, the symbol of the divine presence - the Shekinah - rested; and hence, it was natural to say that God would enter through those gates. In other words, the cover of the ark was regarded as his abode - His seat - His throne; and, as thus occupying the mercy-seat, He was about to enter the place of His permanent abode. Compare Exodus 25:17, Exodus 25:20, Exodus 25:22.