Exodus 20:24

For the worship of Jehovah, the God of heaven, Israel needed only an altar, on which to cause its sacrifices to ascend to God. The altar, as an elevation built up of earth or rough stones, was a symbol of the elevation of man to God, who is enthroned on high in the heaven; and because man was to raise himself to God in his sacrifices, Israel also was to make an altar, though only of earth, or if of stones, not of hewn stones. "For if thou swingest thy tool (חרב lit., sharpness, then any edge tool) over it (over the stone), thou defilest it" (Exo 20:25). "Of earth:" i.e., not "of comparatively simple materials, such as befitted a representation of the creature" (Schultz on Deut 12); for the altar was not to represent the creature, but to be the place to which God came to receive man into His fellowship there. For this reason the altar was to be made of the same material, which formed the earthly soil for the kingdom of God, either of earth or else of stones, just as they existed in their natural state; not, however, "because unpolished stones, which retain their true and native condition, appear to be endowed with a certain native purity, and therefore to be most in harmony with the sanctity of an altar" (Spencer de legg. Hebr. rit. lib. ii. c. 6), for the "native purity" of the earth does not agree with Gen 3:17; but because the altar was to set forth the nature of the simple earthly soil, unaltered by the hand of man. The earth, which has been involved in the curse of sin, is to be renewed and glorified into the kingdom of God, not by sinful men, but by the gracious hand of God alone. Moreover, Israel was not to erect the altar for its sacrifices in any place that it might choose, but only in every place in which Jehovah should bring His name to remembrance. וגו שׁם הז…

All things being prepared for the solemn promulgation of the divine law, we have, in this chapter, I. The ten commandments, as God himself spoke them upon mount Sinai (v. 1-17), as remarkable a portion of scripture as any in the Old Testament. II. The impressions made upon the people thereby (Exo 20:18-21). III. Some particular instructions which God gave privately to Moses, to be by him communicated to the people, relating to his worship (Exo 20:22, etc.).