And Moses wrote all the words of the LORD, and rose up early in the morning, and builded an altar under the hill, and twelve pillars, according to the twelve tribes of Israel.
Moses wrote all the words of the Lord. It is not said where he wrote them, the public register having been mentioned already (Exodus 17:14), in which it seems that, by the special appointment of God, all incidents of public interest or sacred importance, especially His marvelous interpositions, and the revelations of His will and worship, were recorded. The next day preparations were made for having it solemnly ratified, by building an altar and twelve pillars; the altar representing God, and the pillars the tribes of Israel-the two parties in this solemn compact-while Moses acted as typical mediator.
The altar was erected х tachat (H8478) haahaar (H2022)] under (at the base of) the mount, not the hill, as it is erroneously called. х matseebaah (H4676) pillar, a cippus (cf. Genesis 28:18; Genesis 28:22; Isaiah 19:19).] The twelve pillars were set up probably around the altar, which, having been erected in the manner and of the material prescribed (Exodus 20:24), became a temporary place where the presence and blessing of the Lord were enjoyed by the people; and the position of the twelve stones would be ranged in such regular order that they were recognized as representing the respective tribes.
'An altar was a stepping-stone by which man ascended to God, and on which he offered the gifts which he presented to God. It was therefore necessary that the altar should be erected by man himself. When Yahweh came down-not to receive gifts and sacrifices from the people, but to give them laws and promises-Sinai was the altar on which He revealed Himself. The people durst not ascend Mount Sinai to offer their gifts to God; it was necessary, therefore, that they should build an altar themselves, which should bear the same relation to Sinai as the work of man to the work of God. At the same time its connection was to be made known by the fact that it was constructed of earth and unhewn stones' (Kurtz).