Commentaries:
This late spring holy day must be counted. God instructs us to count 50 days from the day that the wavesheaf was offered. This explains why this day is commonly called Pentecost, which means "count fifty." The Sabbath (verse 15), the day after which we start to count, is not an annual holy day, but the weekly Sabbath that falls during Unleavened Bread. We know this because Pentecost must be counted every year. If this Sabbath were an annual Sabbath, Pentecost would always fall on a fixed date. It always falls on the same day of the week—the first day, Sunday—because one begins to count on a Sunday.
Earl L. Henn
Holy Days: Pentecost