Middos, Chapter 3, Mishnah 4. Our chapter has been leading us through the mizbeach and its measurements and features. The Mishnah now turns from dimensions to substance: the kind of stone out of which the altar and its ramp were fashioned, the restrictions on handling that stone, and the routine by which the structure was kept up.
Where the stones came from
"Echad avnei hakevesh" and "echad avnei hamizbeach": the stones of the ramp (kevesh) and those of the altar itself came from a single source, "mibik'at Beit Kerem," the valley of Beit Kerem in the vicinity of Yerushalayim. One quarry served both, because the rock found there was remarkably smooth, and smoothness was exactly what the avodah required.
"Vechofrin lemata mehabetulah." They would search out virgin ground, soil that had never been worked by human hands, never farmed, never built upon, and they would dig down beneath that untouched layer. "Umevi'im misham avanim shelemot": from there they extracted whole stones, smooth and free of any crack or fissure.
Such a demand originates in a pasuk: "Avanim shelemot," continues the verse, "tivneh et mizbach Hashem Elokecha," out of intact stones is the altar of Hashem your God to be erected. The term "shelemot," meaning whole or complete, teaches that any stone carrying a fissure or a chip is unfit for the job.
Iron may never touch them
"Shelo hunaf aleihen barzel, shehabarzel posel benegi'ah." No iron was ever raised over these stones. Iron disqualifies by mere contact: once an iron implement has touched a stone, that stone can no longer be used in building the mizbeach or the ramp.
Here too a pasuk stands behind the halachah: "Uvanita sham mizbeach l'Hashem Elokecha," you shall erect there an altar to Hashem your God, and it is to be a "mizbach avanim," an altar of stone, concerning which the Torah warns, "lo tanif aleihem barzel," do not lift iron over them.
"Ufegimah bechol davar." As for the disqualification of a nick, that is not limited to iron. A stone that became chipped or cracked by anything at all, iron or any other material, is unfit for the mizbeach.
When a single stone is damaged
"Nifgemah achat mehen": should one of the stones develop a nick once it was already in place, "hi pesulah," that single stone alone loses its fitness and has to be pulled out and exchanged, while "vechulan kesherot," all the others retain their validity. The altar as a structure is not forfeited. As soon as the damaged stone is removed and an intact one installed in its spot, the mizbeach may be used again.
Whitewashing the mizbeach
"Umelabnim otan pa'amayim bashanah." The walls and the top surface of the mizbeach were coated with white plaster, and the coating was renewed twice a year so that it would look beautiful. "Achat baPesach ve'achat baChag": once before Pesach and once before Sukkot.
"Vehaheichal pa'am achat baPesach." The exterior of the Heichal building, by contrast, was whitewashed only once a year, before Pesach. The reason for the difference is wear and tear. The mizbeach was in constant use: blood was thrown against it, the kohanim walked upon it and handled it all day long. The Heichal walls suffered nothing comparable, so an annual coating sufficed.
Rebbi: every Friday as well
"Rabbi Meir omer, Rebbi omer": according to Rebbi, the two annual coatings were not the extent of the maintenance. "Kol erev Shabbat," every Friday, in readiness for Shabbat, "melabnim oto bemapa," they would brighten it up with a cloth, "mipnei hadamim," on account of the blood that had been cast against it throughout the week.
"Lo hayu sadin otan": the plaster was never troweled smooth "bekapis shel barzel," with an iron implement, "shema yiga veyifsol," for fear that the metal would come into contact with a stone left uncovered and thereby ruin it. Iron tools were kept entirely away from this work.
Why iron is excluded
"Shehabarzel nivra": the Mishnah concludes by explaining the logic of the entire prohibition. Iron was brought into the world "lekhatzer yamav shel adam," in a manner that cuts a person's life short, for it is out of iron that weaponry is forged. The altar is the opposite: "vehamizbeach nivra leha'arich yamav shel adam," it exists to extend a person's years, since through it he receives kaparah, atonement for his averot.
"Eino din": there is no justice in it, "sheyunaf hamekatzer al hama'arich," that what curtails life should be swung above what prolongs it.