שִׁבְעַ֣ת יָמִ֗ים תָּחֹג֙ לַיהוָ֣ה אֱלֹהֶ֔יךָ בַּמָּק֖וֹם אֲשֶׁר־יִבְחַ֣ר יְהוָ֑ה כִּ֣י יְבָרֶכְךָ֞ יְהוָ֣ה אֱלֹהֶ֗יךָ בְּכֹ֤ל תְּבוּאָֽתְךָ֙ וּבְכֹל֙ מַעֲשֵׂ֣ה יָדֶ֔יךָ וְהָיִ֖יתָ אַ֥ךְ שָׂמֵֽחַ׃
זיבן טעג זאָלסטו האַלטן יָום-טובֿ צו ה׳ דײַן גאָט אין דעם אָרט װאָס גאָט װעט אױסדערװײלן; װאָרום ה׳ דײַן גאָט װעט דיך בענטשן אין דײַן גאַנצן אײַנקום, און אין יעטװעדער טואונג פֿון דײַנע הענט, און װעסט זײַן לױטער פֿרײלעך.
Rashi
והיית אך שמח ONLY BE REJOICED — According to its plain sense this is not the expression of a command but expresses an assurance: “thou will be rejoicing”. But according to the Halachic interpretation they (the Rabbis) derived from here that the night before the last day of the festival (that preceding the eighth day) is to be included in the obligation of rejoicing (Sukkah 48a; cf. Sifrei Devarim 142:4).
Ibn Ezra
you [singular] shall celebrate i.e., you shall perform the sacrifice. This either denotes the community collectively, or it refers to the individual, who may offer burnt-offerings and peace-offerings. The word He blesses you [singular] provides evidence for the latter interpretation, as if to say: You shall do this, because God has blessed you. Scripture adds all your crops , to specify that the blessing refers to the crops that the land has produced,
Sforno
כי יברכך, so that you will have a great deal of gathering in to do, and as a result, the poor will also find much to collect.