Yitro: Rishonim: Mitzvah 40 – Concept 302

“And when you make for Me an altar of stones, do not build them hewn, for you will have raised your sword over it and desecrated it.” (Exodus 20:22) We may not build the Altar with stones hewn by metal. (Rambam, Hilchot Beit HaBechirah – The Laws of the Temple)

This was forbidden so that people would not make some kind of image of the parts of the stone that had been discarded and make them part of their flooring, their mosaic floors. (Rambam, Morah Nevuchim – Guide For The Perplexed 3:45)

Using instruments that are instruments of war to fashion the stones for an altar, which symbolizes peace, would seem a contradiction in terms. (Nachmanides)

Eisav’s power derives from his father’s blessing, “You will survive by the sword.” (Genesis 27:40) At the same time, God is on record repeatedly as saying that He hates Eisav and what Eisav stands for. (Malachi 1:3) Eisav is the antithesis of the altar. (Rabbeinu Bachya)