Deuteronomy 27:5
And there shalt thou build an altar unto the LORD thy God, an altar of stones: thou shalt not lift up any iron tool upon them. And there shalt thou build an altar unto the LORD thy God, an altar of stones: thou shalt not lift up any iron tool upon them.
The command is to build an altar to the Lord of whole, unhewn stones, with no iron tool lifted to shape them. It was to be carried out after passing over Jordan on entering the promised land, before taking possession of it, with the altar set on Mount Ebal in connection with the gathering at Mounts Ebal and Gerizim. There Israel was to set up plastered stones inscribed with the commandments of God, offer burnt and peace offerings on the altar, and eat, worship, and rejoice before God in solemn recognition of His law as a renewal of covenant loyalty.
The exact, specific directions show particular care for a forgetful people, stating plainly the blessings of obedience and the principles of the law of God's kingdom so that minds are not left in ignorance and uncertainty. The words were spoken not by a human voice but by Christ Himself enshrouded in the pillar of cloud, to keep Israel from forgetting and to remind them that obedience to God's commandments is for present and future good, bringing prosperity, while disobedience results in a curse. This involved a repetition of the law from two prominent positions, with the advantages of the blessing pronounced from Mount Gerizim as the mount of blessings and the disadvantages of the curse pronounced from Mount Ebal as the mount of curses.
Standing on the mountain where the curse was pronounced, the altar signified that Israel had rightly incurred the consequences of breaking God's law, and the sacrifices offered there represented Christ's atonement by which the curse would not be visited on them. These Scriptures lay a never-ceasing obligation on all blessed with life, health, and temporal and spiritual advantages to publicly acknowledge His special favor, so that God's name will be glorified as a testimony that His Word is verity and truth.