As God intended in the tabernacle to manifest his presence among his people, so there they were to pay their devotions to him, not in the tabernacle itself (into that only the priests entered as God's domestic servants), but in the court before the tabernacle, where, as common subjects, they attended. There an altar was ordered to be set up, to which they must bring their sacrifices, and on which their priests must offer them to God: and this altar was to sanctify their gifts. Here they were to present their services to God, as from the mercy-seat he gave his oracles to them; and thus a communion was settled between God and Israel. Moses is here directed about, 1. The dimensions of it; it was square, Exo 27:1. 2. The horns of it (Exo 27:2), which were for ornament and for use; the sacrifices were bound with cords to the horns of the altar, and to them malefactors fled for refuge. 3. The materials; it was of wood overlaid with brass, Exo 27:1, Exo 27:2. 4. The appurtenances of it (Exo 27:3), which were all of brass. 5. The grate, which was let into the hollow of the altar, about the middle of it, in which the fire was kept, and the sacrifice burnt; it was made of network like a sieve, and hung hollow, that the fire might burn the better, and that the ashes might fall through into the hollow of the altar, Exo 27:4, Exo 27:5. 6. The staves with which it must be carried, Exo 27:6, Exo 27:7. And, lastly, he is referred to the pattern shown him, Exo 27:8.

Now this brazen altar was a type of Christ dying to make atonement for our sins: the wood would have been consumed by the fire from heaven if it had not been secured by the brass; nor could the human nature of Christ have borne the wrath of God if it had not been supported by a divine power. Christ sanctified himself for his church, as their altar (Joh 17:19), and by his mediation sanctifies the daily services of his people, who have also a right to eat of this altar (Heb 13:10), for they serve at it as spiritual priests. To the horns of this altar poor sinners fly for refuge when justice pursues them, and they are safe in virtue of the sacrifice there offered.

Thou shalt make an altar - מזבח mizbeach, from זבח zabach, to slay: Septuagint, θυσιαστηριον, from θυσιαζω, to sacrifice or from θυω to kill, etc. See Clarke's note on Gen 8:20.

Four square - As this altar was five cubits long and five broad, and the cubit is reckoned to be twenty-one inches, hence it must have been eight feet nine inches square, and about five feet three inches in height, the amount of three cubits, taken at the same ratio.

And thou shall make an altar of shittim wood,.... This is a different altar from that made of earth before the tabernacle was built, Exo 20:24 and from the altar of incense, Exo 30:1 this was to offer burnt offerings on, and was placed at the door of the tabernacle, in the court of the people, where they brought their sacrifices to the priests to offer for them: it stood in the open air, as it was proper it should, that the smoke or the sacrifices might ascend up and scatter. This altar was not typical of the altar of the heart; though indeed all the saints are priests, and every sacrifice of theirs should come from the heart, and particularly love, which is more than all burnt offerings; but the heart is not this altar of brass to bear the fire of divine wrath, which none can endure; nor does it sanctify the gift, it being itself impure: nor of the Lord's table, or the table on which the Lord's supper is set; that is a table, and not an altar, a feast, and not a sacrifice; is not greater than the gift, nor does it sanctify: nor of the cross or Christ, on which he died, bore the sins or his people, and sanctified them by his blood; but of Christ himself, who by his office as a priest, his human nature is the sacrifice, and his divine nature the altar; and he is that altar believers in him have a right to eat of, Heb 13:10 his divine nature is greater than the human, is the support of it, which sanctifies and gives it virtue as a sacrifice, and which makes the sacrifices of all his people acceptable to God. This altar of burnt offering is said to be made of "shittim wood", a wood incorruptible and durable; Christ, as God, is from everlasting to everlasting; as man, though he once died, he now lives for evermore, and never did or will see corruption; his priesthood is an unchangeable priesthood, and passes not from one to another, and particularly his sacrifice is of a continual virtue and efficacy:

five cubits long, and five cubits broad: the altar shall be square: as to the length and breadth of it, which were alike, two yards and a half each, according to the common notion of a cubit. The altars of the Heathens were made in imitation of this, they were square as this was. Pausanias makes mention of an altar of Diana, that was "square", sensibly rising up on high. And this figure may denote the perfection of Christ's sacrifice, and the permanency of it; though the altars in Solomon's temple, and in the visions of Ezekiel, are much larger, and which also were square, Ch2 4:1. Christ's sacrifice is large and extensive, making satisfaction for all his people, and for all their sins; and he is an altar large enough for all their sacrifices to be offered up to God with acceptance:

and the height thereof shall be three cubits; a proper height for a man to minister at; for as Aben Ezra observes, the height of a man is but four cubits ordinarily; so that a man serving at the altar would be a cubit, or half a yard more above it, and would have command of doing on it what he had to do.