Seven weeks shalt thou number unto thee: begin to number the seven weeks from such time as thou beginnest to put the sickle to the corn.
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.
The three yearly feasts kept up communion between God and His people and preserved the face of religion in the nation. One week only was festival, yet their solemn preparation before and serious reflection afterward amounted to observance of the whole month; thus the ceremonies themselves became the means by which God's truth took root in their hearts.
AI summary
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...