Kommentar zu Dewarim 12:13

השמר לך TAKE HEED TO THYSELF [LEST THOU OFFER THY BURNT OFFERINGS IN EVERY PLACE THAT THOU SEEST] — This negative form of the positive command in v. 11, is stated in order to attach a negative command (לאו) to this matter (Sifrei Devarim 70:1).

בכל מקום אשר תראה, “in any place that you see.” This is a negative commandment; however, at the bidding of a legitimate prophet, under special circumstances, sacrifices may be offered on an altar outside the Temple such as Elijah’s at Mount Carmel when the purpose was to delegitimize the prophets of the Baal.

This places a negative commandment over the matter. Rashi is answering the question: Scripture had already written above (v. 11), “It is there you shall bring,” which implies only there and nowhere else. Why does it need to say again, “Take heed”? Rashi answers: “This places a negative commandment over the matter.”

V. 13. השמר לך. Es ist dies das Verbot, die אזהרה, zu der bereits Wajikra 17. 8 u. 9 mit כרת verpönten שחיטה והעלאה בחוץ (siehe daselbst) nach dem Kanon: כל מקום שנאמר השמר פן ואל אינו אלא לא תעשה (Sebachim 106 a).

השמר לך פן תעלה עולותיך בכל מקום, “Take heed not to offer your burnt offerings at any place;” the reason why the Torah is so insistent that offerings not be brought other than at a central location, is that seeing the Israelites are supposed to make at least three pilgrimages a year to the Temple in Jerusalem, if they were legally able to offer the sacrifices that they need to offer also on private altars, many would use that as an excuse not to make the pilgrimages to Jerusalem. Once they would get into the habit to offer sacrifices to Hashem on private altars, it would be a small step to also offer some sacrifices, such as calves, to other “deities.” [As we saw once Jerobam erected these calves by blocking the highways to Jerusalem to pilgrims. (Compare Kings I chapter 12) Ed.]

בכל מקום אשר תראה IN EVERY PLACE THAT “THOU” SEEST — i.e., that enters thy mind, but thou mayest offer anywhere by the command of a prophet, as, for instance, Elijah did on Mount Carmel (1 Kings 18:21 ff.) (Sifrei Devarim 70:3).

However, you may bring an offering by prophetic instruction, etc. Rashi is answering the question: Why is it written, “you envision”? It only needs to say, “anywhere.” The answer is: The words, “you envision,” teach us that bringing sacrifices is forbidden only in a place where you envision. However, you may bring an offering by prophetic instruction, etc.