Four-square - That is, on the upper or under surface, as it showed four equal sides; but it was twice as high as it was broad, being twenty-one inches broad, and three feet six inches high. It was called, not only the altar of incense, but also the golden altar, Numbers 4:11. For the crown, horns, staves, etc., see on the altar of burnt-offering, Exodus 27:1 (note), etc.

A cubit [shall be] the length thereof, and a cubit the breadth thereof; foursquare shall it be: and two cubits [shall be] the height thereof: the horns thereof [shall be] (b) of the same.
(b) Of the same wood and matter.

A cubit shall be the length thereof, and a cubit the breadth thereof, four square shall it be,.... It was one Jewish square cubit, which is in surface, according to Bishop Cumberland, three English square feet, and about forty seven square inches; which may denote the solidity, perfection, and extensiveness of Christ's priesthood, it being unchangeable, firm, and lasting; and which passes not from one to another, and the which makes something perfect, which the law and priesthood of Aaron could not, even perfects for ever them that are sanctified; and is very extensive; the virtue of it reaches to all the elect of God, from the beginning of the world to the end of it; not his sacrifice only, but his intercession, which is principally respected; that is made for all the people of God, in all places, and in all ages, and for all things for them, both for this life, and that which is to come:
and two cubits shall be the height thereof; so that it was as high again as it was long and broad: Christ, our interceding high priest, is made higher than the heavens:
the horns thereof shall be of the same; of the same wood the altar itself was made: these were a sort of spires that rose up at the four corners of the altar; and the Targum of Jonathan paraphrases the words,"and of it its horns shall be erect;''which were chiefly for decoration and ornament; and may denote the honour and glory of Christ, as well as his power and ability to save, to the uttermost, all that come to God by him, or lay hold upon him, since he ever lives to make intercession.

foursquare--the meaning of which is not that it was to be entirely of a cubical form, but that upon its upper and under surface, it showed four equal sides. It was twice as high as it was broad, being twenty-one inches broad and three feet six inches high. It had "horns"; its top or flat surface was surmounted by an ornamental ledge or rim, called a crown, and it was furnished at the sides with rings for carriage. Its only accompanying piece of furniture was a golden censer or pan, in which the incense was set fire to upon the altar. Hence it was called the altar of incense, or the "golden altar" [Exodus 39:38; Exodus 40:26], from the profuse degree in which it was gilded or overlaid with the precious metal. This splendor was adapted to the early age of the church, but in later times, when the worship was to be more spiritual, the altar of incense is prophetically described as not of gold but of wood, and double the size of that in the tabernacle, because the church should be vastly extended (Malachi 1:11).