(Ibid. 20) "that it is not a fruitful tree": This is a barren tree. If in the end we include (to be cut down for the siege even) a fruitful tree, what is the intent of "that it is not a fruitful tree"? We are hereby taught that a barren tree takes precedence (to being cut down) to a fruitful tree (if only one is needed for the siege). I might think that this holds true even if the barren tree is worth more, as per the words of R. Elazar b. R. Shimon; it is, therefore, written "Only" (to exclude such an instance).
(דברים כ כ) רַק עֵץ אֲשֶׁר תֵּדַע – זֶה אִילַן מַאֲכָל.
(Devarim 20:20) "Only a tree that you know": This is a fruitful tree. (Ibid. 19) "to come before you into the siege": Cut it down.
כִּי לֹא עֵץ מַאֲכָל הוּא – זֶה אִילַן סְרָק. אִם סוֹפֵנוּ לְרַבּוֹת אֶת אִילַן מַאֲכָל, מַה תַּלְמוּד לוֹמַר עֵץ מַאֲכָל? מְלַמֵּד שֶׁאִילַן סְרָק קוֹדֵם לְאִילַן מַאֲכָל. יָכוֹל אֲפִלּוּ מְעֻלֶּה בְּדָמִים, וּכְדִבְרֵי רַבִּי אֶלְעָזָר בְּרַבִּי שִׁמְעוֹן? תַּלְמוּד לוֹמַר: אֹתוֹ תַשְׁחִית וְכָרָתָּה,
(Ibid. 20) "that it is not a fruitful tree": This is a barren tree. If in the end we include (to be cut down for the siege even) a fruitful tree, what is the intent of "that it is not a fruitful tree"? We are hereby taught that a barren tree takes precedence (to being cut down) to a fruitful tree (if only one is needed for the siege). I might think that this holds true even if the barren tree is worth more, as per the words of R. Elazar b. R. Shimon; it is, therefore, written "Only" (to exclude such an instance).
עוֹשֶׂה אַתָּה מִמֶּנּוּ תְּיָקִים וּנְדַבְיָאוֹת.
"and you shall cut": Make of it barriers and siegeworks.
וּבָנִיתָ מָצוֹר עַל הָעִיר – עוֹשֶׂה אַתָּה לָהּ מִינֵי מַטְרְנִיָּאוֹת,
"and build the siege": Make siege engines for it.
מֵבִיא אַתָּה לָהּ מִינֵי בַּלִּסְטְרָאוֹת.
"against the city": Bring up catapults against it.
עַד רִדְתָּהּ – וַאֲפִלּוּ בְּשַׁבָּת.
"until it is subdued": even on the Sabbath. This is one of the things expounded by Shammai the elder.