All the feasts of Israel were important, and the Lord wanted Israel to observe them at certain times, including the Feast of Weeks, even showing them when they were to begin the countdown for when the feast would start,

“You shall count seven weeks for yourself; begin to count the seven weeks from the time you begin to put the sickle to the grain” (Deuteronomy 16.9).

There is that number seven again.

Seven means something to the Lord, in many cases showing completeness.

Thus, from the Passover and the Feast of Unleavened Bread, Israel counted seven weeks, plus a day (Leviticus 23.15, 16), creating what we call in the New Testament, the Day of Pentecost.