9 Seven weeks shalt thou number unto thee: from the time thou beginnest to put the sickle to the standing grain shalt thou begin to number seven weeks. 10 And thou shalt keep the feast of weeks unto Jehovah thy God with a tribute of a freewill-offering of thy hand, which thou shalt give, according as Jehovah thy God blesseth thee: 11 and thou shalt rejoice before Jehovah thy God, thou, and thy son, and thy daughter, and thy man-servant, and thy maid-servant, and the Levite that is within thy gates, and the sojourner, and the fatherless, and the widow, that are in the midst of thee, in the place which Jehovah thy God shall choose, to cause his name to dwell there.

Matthew Henry's Commentary on Deuteronomy 16:9-11

Commentary on Deuteronomy 16:1-17

(Read Deuteronomy 16:1-17)

The laws for the three yearly feasts are here repeated; that of the Passover, that of the Pentecost, that of Tabernacles; and the general law concerning the people's attendance. Never should a believer forget his low estate of guilt and misery, his deliverance, and the price it cost the Redeemer; that gratitude and joy in the Lord may be mingled with sorrow for sin, and patience under the tribulations in his way to the kingdom of heaven. They must rejoice in their receivings from God, and in their returns of service and sacrifice to him; our duty must be our delight, as well as our enjoyment. If those who were under the law must rejoice before God, much more we that are under the grace of the gospel; which makes it our duty to rejoice evermore, to rejoice in the Lord always. When we rejoice in God ourselves, we should do what we can to assist others also to rejoice in him, by comforting the mourners, and supplying those who are in want. All who make God their joy, may rejoice in hope, for He is faithful that has promised.