John Gill Commentary Deuteronomy 16:15

"Seven days shalt thou keep a feast unto Jehovah thy God in the place which Jehovah shall choose; because Jehovah thy God will bless thee in all thine increase, and in all the work of thy hands, and thou shalt be altogether joyful." — Deuteronomy 16:15 (ASV)

Seven days you shall keep a solemn feast unto the Lord your
God
The feast of tabernacles still spoken of:

in the place which the Lord your God shall choose :
the city of Jerusalem:

because the Lord your God shall bless you in all your increase, and in
all the works of your hands ;
both in the increase of their fields, vineyards, and oliveyards, and also in their several handicraft trades and occupations they were employed in; so Aben Ezra interprets all the works of their hands of merchandise and manufactories:

therefore you shall surely rejoice ;
extremely, heartily, and sincerely, and not fail to express joy on this occasion, and manifest it by a generous freewill offering to the Lord, and a bountiful entertainment for himself, his family, friends, and others.