Here is the institution of the feast of pentecost, or weeks, as it is called (Deu 16:9), because it was observed fifty days, or seven weeks, after the passover. It is also called the feast of harvest, Exo 23:16. For as the presenting of the sheaf of first-fruits was an introduction to the harvest, and gave them liberty to put in the sickle, so they solemnized the finishing of their corn-harvest at this feast. 1. Then they offered a handful of ears of barley, now they offered two loaves of wheaten bread, Lev 23:17. This was leavened. At the passover they ate unleavened bread, because it was in remembrance of the bread they ate when they came out of Egypt, which was unleavened; but now at pentecost it was leavened, because it was an acknowledgment of God's goodness to them in their ordinary food, which was leavened. 2. With that sheaf of first-fruits they offered only one lamb for a burnt-offering, but with these loaves of first-fruits they offered seven lambs, two rams, and one bullock, all for a burnt-offering, so giving glory to God, as the Lord of their land and the Lord of their harvest, by whose favour they lived and to whose praise they ought to live. They offered likewise a kid for a sin-offering, so taking shame to themselves as unworthy of the bread they ate, and imploring pardon for their sins, by which they had forfeited their harvest-mercies, and which they had been guilty of in the receiving of them. And lastly, two lambs for a sacrifice of peace-offerings, to beg a blessing upon the corn they had gathered in, which would be neither sure nor sweet to them without that blessing, Hag 1:9. These were the only peace-offerings that were offered on the behalf of the whole congregation, and they were reckoned most holy offerings, whereas other peace-offerings were but holy. All these offerings are here appointed, Lev 23:18-20. 3. That one day was to be kept with a holy convocation, Lev 23:21. It was one of the days on which all Israel was to meet God and one another, at the place which the Lord should choose. Some suggest that whereas seven days were to make up the feast of unleavened bread there was only one day appointed for the feast of pentecost, because this was a busy time of the year with them, and God allowed them speedily to return to their work in the country. This annual feast was instituted in remembrance of the giving of the law upon mount Sinai, the fiftieth day after they came out of Egypt. That was the feast which they were told in Egypt must be observed to God in the wilderness, as a memorial of which ever after they kept this feast. But the period and perfection of this feast was the pouring out of the Spirit upon the apostles on the day of this feast (Act 2:1), in which the law of faith was given, fifty days after Christ our passover was sacrificed for us. And on that day (as bishop Patrick well expresses it) the apostles, having themselves received the first-fruits of the Spirit, begat three thousand souls, through the word of truth, and presented them, as the first-fruits of the Christian church, to God and the Lamb.
To the institution of the feast of pentecost is annexed a repetition of that law which we had before (Lev 19:9), by which they were required to leave the gleanings of their fields, and the corn that grew on the ends of the butts, for the poor, Lev 23:22. Probably it comes in here as a thing which the priests must take occasion to remind the people of, when they brought their first-fruits, intimating to them that to obey even in this small matter was better than sacrifice, and that, unless they were obedient, their offerings should not be accepted. It also taught them that the joy of harvest should express itself in charity to the poor, who must have their due out of what we have, as well as God his. Those that are truly sensible of the mercy they receive from God will without grudging show mercy to the poor.

Neither shalt thou gather any gleaning - See the note on Lev 19:9.

And when ye reap the harvest of your land,.... This law is repeated from Lev 19:9; and as Aben Ezra observes, the feast of weeks being the feast of the firstfruits of the wheat harvest, it is repeated, that they might not forget what God had commanded them to do at that time, namely, to leave somewhat for the poor; and the Jewish writers (a) observe, that this law, being put among the solemn feasts of the passover, pentecost, and tabernacles, and the beginning of the year, and the day of atonement, teaches, that he that observes it, and leaves the corner of the field and the gleanings to the poor, it is as if he built the sanctuary, and offered his sacrifices in the midst of it; but a much better reason may be given for it, which was, to teach them that when they expressed their thankfulness to God, they should exercise charity and liberality to the poor:

thou shalt not make clean riddance of the corners of thy field when thou reapest, neither shalt thou gather any gleaning of thy harvest: See Gill on Lev 19:9,

thou shalt leave them unto the poor, and to the stranger: I am the Lord your God; See Gill on Lev 19:10.

(a) In Torat Cohenim, apud Yalkut in loc. & Jarchi.

thou shalt not make clean riddance of the corners of thy field when thou reapest, &c.--(See on Lev 19:9). The repetition of this law here probably arose from the priests reminding the people, at the presentation of the first-fruits, to unite piety to God with charity to the poor.