Le Deutéronome 12:17 Commentaire : Rashi, Chizkuni, Ibn Ezra & Siftei Chakhamim

לא תוכל THOU MAYEST NOT [EAT WITHIN THY GATES THE TITHE OF THY CORN etc.] — Scripture thereby intends to attach to this matter (the eating of מעשר בכור etc. outside the walls of Jerusalem) a negative command also (the positive command being contained in v. 11).

לא תוכל לאכול, “you cannot eat;” Rashi quotes Rabbi Joshua son of Korchah as saying that the words לא תוכל, do not mean that the Levites are physically unable to eat the tithes in their homes or towns, but that they are forbidden to do so. [What applies to the first tithe given to the Levite also applies to the “second” tithe that the Israelite during the respective years may consume himself but only in Jerusalem, or other designated town housing the Tabernacle at the time. If such second tithe has been redeemed by the farmer, then the money received must be spent in Jerusalem or its equivalent, for food, drink or clothing and such for the farmer and his family. The same applies to other gifts given to the priests, such as the firstlings of the harvest each year. The “gift” known as t’rumah, from the grain fields, may be eaten in the priest’s home by himself and his family and household.] According to Rashi on Joshua 15,63, the words ולא יכלו בני יהודה להורישם, “and the members of the tribe of Yehudah were unable to dislodge the Jebusite from their city (Jerusalem)” are also to be understood as a prohibition. i.e. the covenant made between Avraham and Avimelech for four generations, had not yet expired, so that G-d had not yet given permission for the Israelites to conquer that part of the land of Israel. The inhabitants of that city at that time were not Jebusites, i.e. Canaanites, to whom that covenant did not apply, but were Philistines to whom it did apply.)

to eat within your gates the tithe of your grain… Scripture addresses the Levites (and, according to many, also the common Israelites, apropos the second tithe);

לא תוכל THOU MAYEST NOT (lit., thou canst not) [EAT etc.] — Rabbi Joshua the son of Korcha said: You can, but you are not allowed to (i.e. לא תוכל does not mean: you are unable for some reason or another to do so, but it expresses the inability to do it because of a legal restriction). A similar case we have in (Joshua 15:63) “As to the Jebusites, the inhabitants of Jerusalem, the children of Judah could not drive them out” — they could have done so, but they were not allowed to (Sifrei Devarim 72:1); because Abraham had made a covenant with them when he bought from them the cave of Machpelah that they would be spared at the conquest of the Land. — As a matter fact they were not Jebusites but Hittites (the people mentioned in Genesis 23 at the purchase of the cave), but they were called Jebusites after the city the name of which was Jebus. Thus is it explained in the Pirkei DeRabbi Eliezer 36. And this is the meaning of what is stated, that when David was about to drive out the Jebusites, they said to him (II Samuel 5:6) “Except thou take away the blind and the lame [thou shalt not come in hither]” — by “the blind and the lame” they meant the idols (that stood at the gates) upon which they had written the oath which Abraham had taken.