The altar (mizbeach) must be built only from natural stones, not stones hewn by iron or other metal tools. The Torah explicitly forbids the use of iron, symbolically linked to instruments of war and death, for constructing the altar, which is an instrument of peace and atonement.

Rambam explains that the altar’s sanctity would be compromised by contact with iron. The Sages noted the contrast: iron shortens life, while the altar lengthens it by bringing atonement. Therefore, they must not be joined.

This mitzvah emphasizes that holiness must be preserved in every aspect of the Temple’s service, including the materials and methods of construction. It symbolizes the separation of violence and destruction from sanctity and peace.

Commentary & Classical Explanation:

• Rambam (Hilchot Beit HaBechirah 1:13): States that stones of the altar must not be touched by iron or any tool.
• Sefer HaChinuch (Mitzvah 40): Explains that the altar brings life, while iron brings death; mixing the two profanes sanctity.
• Rashi (Exodus 20:22): Notes that iron is used to shorten life, while the altar was made to prolong it—thus they must not come together.
• Ramban (Exodus 20:22): Adds that holiness demands separation from the instruments of destruction.
• Talmud (Middot 3:4; Makkot 11a): Teaches that the stones were taken whole from quarries without iron tools, even during King Solomon’s Temple.