Deuteronomy 27:5-10

there shalt thou build an altar . . . of whole stones—The stones were to be in their natural state, as if a chisel would communicate pollution to them. The stony pile was to be so large as to contain all the conditions of the covenant, so elevated as to be visible to the whole congregation of Israel; and the religious ceremonial performed on the occasion was to consist: first, of the elementary worship needed for sinful men; and secondly, of the peace offerings, or lively, social feasts, that were suited to the happy people whose God was the Lord. There were thus, the law which condemned, and the typical expiation—the two great principles of revealed religion.