“You shall count seven weeks. Begin to count the seven weeks from the time the sickle is first put to the standing grain.
9. Seven weeks shalt thou number. It must be observed that the Passover fell in a part of the year when the harvests were beginning to ripen; and consequently the first-fruits, of which I treated under the First Commandment, were then offered. Seven weeks afterwards they celebrated another feast-day, which was called Pentecost, i.e., the fiftieth, by the Greeks.
Much of the communion between God and his people Israel was kept up, and a face of religion preserved in the nation, by the three yearly feasts, the institution of which, and the laws concerning them, we have several times met with already; and here they are repeated. I.
Commenting on Deuteronomy 16:1-17
Seven weeks then shalt thou number unto thee,.... And then another feast was to take place, called from hence the feast of weeks, and sometimes Pentecost, from its being the fiftieth day: begin to number the seven weeks from such time as thou beginnest to put the sickle to the corn; for the sheaf of the wave offering, as the first fruits of barley harvest...