Thou shalt make for it a grate - Calmet supposes this altar to have been a sort of box, covered with brass plates, on the top of which was a grating to supply the fire with air, and permit the ashes to fall through into the siroth or pan that was placed below. At the four corners of the grating were four rings and four chains, by which it was attached to the four horns; and at the sides were rings for the poles of shittim wood with which it was carried. Even on this there is a great variety of opinions.

And thou shalt, make for it a grate of network of brass,.... Or "sieve", as in Amos 9:9, it was a plate of brass with holes in it, to let through either the blood that drained from the parts of the sacrifice, or the ashes of it; for this was the focus or hearth, on which the sacrifice and the wood were laid and burnt: this, according to the Targum of Jonathan on Exodus 38:4 was to receive the coals and bones which fell from the altar: and so may denote the purity of Christ's sacrifice, which was offered up without spot to God, and the use of him as the altar to sanctify our gifts, and take away the sins of our holy things:
and upon the net shalt thou make four brazen rings in the four corners thereof; by which, with chains put into them, the grate was fastened to the four horns of the altar, and the use of them was to let it down and hang in the middle of the altar, and to take it up when there was occasion for it; though some think these rings were not "in" the grate, but "by" it, as the particle may be rendered, a little lower than that, on the sides of the altar; into which the staves after mentioned were put, and with which the altar was carried when removed from place to place.

a grate of network of brass--sunk latticework to support the fire.
four brazen rings--by which the grating might be lifted and taken away as occasion required from the body of the altar.

The altar was to have מכבּר a grating, רשׂת מעשׂה net-work, i.e., a covering of brass made in the form of a net, of larger dimensions that the sides of the altar, for this grating was to be under the "compass" (כּרכּב) of the altar from beneath, and to reach to the half of it (half-way up, Exodus 27:5); and in it, i.e., at the four ends (or corners) of it, four brass rings were to be fastened, for the poles to carry it with. כּרכּב (from כּרכּב circumdedit) only occurs here and in Exodus 38:4, and signifies a border (סבבא Targums), i.e., a projecting framework or bench running round the four sides of the altar, about half a cubit or a cubit broad, nailed to the walls (of the altar) on the outside, and fastened more firmly to them by the copper covering which was common to both. The copper grating was below this bench, and on the outside. The bench rested upon it, or rather it hung from the outer edge of the bench and rested upon the ground, like the inner chest, which it surrounded on all four sides, and in which there were no perforations. It formed with the bench or carcob a projecting footing, which caused the lower half of the altar to look broader than the upper on every side. The priest stood upon this carcob or bench when offering sacrifice, or when placing the wood, or doing anything else upon the altar. This explains Aaron's coming down (ירד) from the altar (Leviticus 9:22); and there is no necessity to suppose that there were steps to the altar, as Knobel does in opposition to Exodus 20:26. For even if the height of the altar, viz., three cubits, would be so great that a bench half-way up would be too high for any one to step up to, the earth could be slightly raised on one side so as to make the ascent perfectly easy; and when the priest was standing upon the bench, he could perform all that was necessary upon the top of the altar without any difficulty.

The grate was set 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 net - work like a sieve, and hung hollow, that the fire might burn the better, and that the ashes might fall through. Now, this brazen altar was a type of Christ dying to make atonement for our sins. Christ sanctified himself for his church as their altar, John 17:19, and by his mediation sanctifies the daily services of his people. To the horns of this altar poor sinners fly for refuge, and are safe in virtue of the sacrifice there offered.