Midrash su Deuteronomio 27:6

8) R. Yochanan b. Zakkai said (Devarim 27:6) "Of whole (shleimoth) stones shall you build the altar of the L–rd your G d, etc.": "stones which make peace" (shalem). Now does this not follow a fortiori: If stones, which do not see, and which do not hear, and which do not speak — because they "make peace" between Israel and their Father in heaven, Scripture writes (Devarim 27:5) "You shall not lift iron over them," then a man who makes peace between a man and his wife, between family and family, between city and city, between country and country, and between one people and another — how much more so will calamity not befall him!

R. Johanan the son of Zakkai said: Scripture states: Thou shalt build the altar of the Lord thy God of unhewn stones (Deut. 27:6), for it will help to achieve peace between the Israelites and their Father in heaven. A logical conclusion may be derived from this. If the stones of the altar, which cannot see or hear or speak, achieve peace between Israel and their Father in heaven, so that the Torah commands that iron should not be wielded over them, how much more so, then, should one who promotes peace between husband and wife, or between a man and his companion, have his days and his years prolonged.

(Exodus, Ibid. 22) "And if an altar of stones you make for Me": R. Yishmael says: Every "if" in the Torah connotes optionality, except for three; (Leviticus 2:14) "And if you offer an offering of first-fruits" — This is mandatory. You say it is mandatory, but perhaps it is optional. (This is not so, for) it is written (Ibid.) "You shall offer the offering of your first-fruits." It is mandatory, not optional. Similarly, (Exodus 22:24) "If you lend money to My people, the poor man with you, etc." This is mandatory. You say it is mandatory, but perhaps it is optional. It is, therefore, written (Devarim 15:8) "Lend shall you lend him." It is mandatory, not optional. Similarly, "And if an altar of stones you make for Me." This is mandatory. You say it is mandatory, but perhaps it is optional. (This is not so,) for it is written (Devarim 27:6) "Of whole stones shall you build the altar of the L rd." It is mandatory and not optional (to build an altar). And what is the intent of "if an altar of stones"? If he wishes to build it of stones, he may do so. (If he wishes to build it) of bricks, he may do so. Now does this not follow a fortiori for the other vessels, viz. If he may vary (i.e., either stones or bricks) for the altar, the more "formidable," how much more so may he do so for other vessels (of lesser formidability) (e.g., the menorah and the table, to make them of silver.) (Exodus 20:22) "Do not build them gazith": "gazith" is "gezuzoth" (hewn,) iron having been lifted upon them. R. Nathan says: I might think that if one built two stones (into the altar) upon which iron had been lifted (that) the entire altar is unfit, it is, therefore, written "Do not build them hewn" — They are unfit, but not the entire altar.