Charles Ellicott Commentary Exodus 34:22

"And thou shalt observe the feast of weeks, [even] of the first-fruits of wheat harvest, and the feast of ingathering at the year`s end." — Exodus 34:22 (ASV)

The feast of weeks. —Called in Exodus 23:16, the feast of harvest, and in the New Testament “the day of Pentecost”—seven weeks after the first day of unleavened bread. (See Note 1 on Exodus 23:16.) The special offering to be made at the feast consisted of two wave loaves of fine flour, baken with leaven (Leviticus 23:17), which were “the first-fruits of the wheat harvest.”

And the feast of ingathering. —Called also the feast of tabernacles (Leviticus 23:34; Deuteronomy 16:13; Deuteronomy 16:16; Deuteronomy 31:10, and other passages), on account of the command to dwell in booths seven days during its continuance (Leviticus 23:42). On the character of the festival see Note 2 on Exodus 23:16.