A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
exo 30:1THE ALTAR OF INCENSE. (Exo. 30:1-38)
thou shalt make an altar to burn incense upon, &c.--Its material was to be like that of the ark of the testimony, but its dimensions very small [Exo 25:10].
exo 30:2foursquare--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" [Exo 39:38; Exo 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 (Mal 1:11).
exo 30:6thou shalt put it before the veil that is by the ark of the testimony--which separated the holy from the most holy place. The altar was in the middle between the table of showbread and the candlestick next the holy of holies, at equal distances from the north and south walls; in other words, it occupied a spot on the outside of the great partition veil, but directly in front of the mercy seat, which was within that sacred enclosure; so that although the priest who ministered at this altar could not behold the mercy seat, he was to look towards it, and present his incense in that direction. This was a special arrangement, and it was designed to teach the important lesson that, though we cannot with the eye of sense, see the throne of grace, we must "direct our prayer to it and look up" [Psa 5:3] (compare Co2 3:14; Heb 10:20; Rev 4:1).
exo 30:7Aaron shall burn thereon sweet incense--literally, "incense of spices"--Strong aromatic substances were burnt upon this altar to counteract by their odoriferous fragrance the offensive fumes of the sacrifices; or the incense was employed in an offering of tributary homage which the Orientals used to make as a mark of honor to kings; and as God was Theocratic Ruler of Israel, His palace was not to be wanting in a usage of such significancy. Both these ends were served by this altar--that of fumigating the apartments of the sacred edifice, while the pure lambent flame, according to Oriental notions, was an honorary tribute to the majesty of Israel's King. But there was a far higher meaning in it still; for as the tabernacle was not only a palace for Israel's King, but a place of worship for Israel's God, this altar was immediately connected with a religious purpose. In the style of the sacred writers, incense was a symbol or emblem of prayer (Psa 141:2; Rev 5:8; Rev 8:3). From the uniform combination of the two services, it is evident that the incense was an emblem of the prayers of sincere worshippers ascending to heaven in the cloud of perfume; and, accordingly, the priest who officiated at this altar typified the intercessory office of Christ (Luk 1:10; Heb 7:25).
every morning . . . at even--In every period of the national history this daily worship was scrupulously observed.
exo 30:8Aaron shall burn incense--seemingly limiting the privilege of officiating at the altar of incense to the high priest alone, and there is no doubt that he and his successors exclusively attended this altar on the great religious festivals. But "Aaron" is frequently used for the whole priestly order, and in later times, any of the priests might have officiated at this altar in rotation (Luk 1:9).
exo 30:9Ye shall offer no strange incense--that is, of a different composition from that of which the ingredients are described so minutely.
exo 30:11When thou takest the sum of the children of Israel, &c.--Moses did so twice, and doubtless observed the law here prescribed. The tax was not levied from women, minors, old men (Num 1:42, Num 1:45), and the Levites (Num 1:47), they being not numbered. Assuming the shekel of the sanctuary to be about half an ounce troy, though nothing certain is known about it, the sum payable by each individual was two and four pence. This was not a voluntary contribution, but a ransom for the soul or lives of the people. It was required from all classes alike, and a refusal to pay implied a wilful exclusion from the privileges of the sanctuary, as well as exposure to divine judgments. It was probably the same impost that was exacted from our Lord (Mat 17:24-27), and it was usually devoted to repairs and other purposes connected with the services of the sanctuary.
exo 30:18Thou shalt . . . make a laver of brass--Though not actually forming a component part of the furniture of the tabernacle, this vase was closely connected with it; and though from standing at the entrance it would be a familiar object, it possessed great interest and importance from the baptismal purposes to which it was applied. No data are given by which its form and size can be ascertained; but it was probably a miniature pattern of Solomon's--a circular basin.
his foot--supposed not to be the pedestal on which it rested, but a trough or shallow receptacle below, into which the water, let out from a cock or spout, flowed; for the way in which all Eastern people wash their hands or feet is by pouring upon them the water which falls into a basin. This laver was provided for the priests alone. But in the Christian dispensation, all believers are priests, and hence the apostle exhorts them how to draw near to God (Joh 13:10; Heb 10:22).
exo 30:23Take thou also . . . principal spices, &c.--Oil is frequently mentioned in Scripture as an emblem of sanctification, and anointing with it a means of designating objects as well as persons to the service of God. Here it is prescribed by divine authority, and the various ingredients in their several proportions described which were to compose the oil used in consecrating the furniture of the tabernacle.
myrrh--a fragrant and medicinal gum from a little known tree in Arabia.
sweet cinnamon--produced from a species of laurel or sweet bay, found chiefly in Ceylon, growing to a height of twenty feet: this spice is extracted from the inner bark, but it is not certain whether that mentioned by Moses is the same as that with which we are familiar.
sweet calamus--or sweet cane, a product of Arabia and India, of a tawny color in appearance; it is like the common cane and strongly odoriferous.
exo 30:24cassia--from the same species of tree as the cinnamon--some think the outer bark of that tree. All these together would amount to one hundred twenty pounds, troy weight.
hin--a word of Egyptian origin, equal to ten pints. Being mixed with the olive oil--no doubt of the purest kind--this composition probably remained always in a liquid state, and the strictest prohibition issued against using it for any other purpose than anointing the tabernacle and its furniture.
exo 30:34the Lord said unto Moses, Take unto thee sweet spices--These were:
stacte--the finest myrrh;
onycha--supposed to be an odoriferous shell;
galbanum--a gum resin from an umbelliferous plant.
frankincense--a dry, resinous, aromatic gum, of a yellow color, which comes from a tree in Arabia, and is obtained by incision of the bark. This incense was placed within the sanctuary, to be at hand when the priest required to burn on the altar. The art of compounding unguents and perfumes was well known in Egypt, where sweet-scented spices were extensively used not only in common life, but in the ritual of the temples. Most of the ingredients here mentioned have been found on minute examination of mummies and other Egyptian relics; and the Israelites, therefore, would have the best opportunities of acquiring in that country the skill in pounding and mixing them which they were called to exercise in the service of the tabernacle. But the recipe for the incense as well as for the oil in the tabernacle, though it receives illustration from the customs of Egypt, was peculiar, and being prescribed by divine authority, was to be applied to no common or inferior purpose.