פירוש על דברים 26:11

ושמחת בכל הטוב AND THOU SHALT REJOICE IN EVERY GOOD THING — From this they (the Rabbis) derived the law that the recital on the occasion of bringing the first fruits is made only during the joyful period of the year — from Pentecost till the Feast of Tabernacles — when a man is gathering in his grain, his fruits, his wine and his oil; but from Tabernacles onwards until Chanucah if he brings these, he does not make the recital (Pesachim 36b).

concerning the words “נותן לך ושמת בטנא,” (from verse 2) the vowel kametz under the letter ל of the word לך was justified as it represented the end of the speech. When the word לך has the vowel kametz under the letter ך, this indicates that it belongs to what came before.

Except during the time of rejoicing, etc. Otherwise, what rejoicing is there that it is written “you shall rejoice, etc.”? It is not eaten by non-kohanim because its laws are derived from terumah [which is forbidden to non-kohanim]? Therefore he explains, “From here they derive, etc.” Therefore, regarding the Levi and the proselyte too, you cannot explain as in parshas Re'ei (above 12:18), that you are obligated to have them rejoice with you, since it is forbidden to them. Therefore he explains that they too are obligated in first fruits (Devek Tov).