"You shall count from the next day after the Shabbat, from the day that you brought the sheaf of the wave offering: seven Shabbats shall be completed; even to the next day after the seventh Shabbat you shall count fifty days." Vayikra 23:15–16 · KWS
The Torah Mitzvah
Fifty days counted from Firstfruits. Two loaves of leavened bread waved.
Shavuot — Hebrew for "weeks," Greek Pentecost for "fiftieth" — is timed off Firstfruits. The household counts seven complete weeks plus one day, fifty days exactly, and the moed lands. Two loaves of leavened bread are waved before YHWH as the firstfruits of wheat Vayikra 23:17. It is a kodesh convocation — work rests, the household gathers.
"All the people perceived the thunderings, the lightnings, the sound of the trumpet, and the mountain smoking." Shemot 20:18 · KWS
The Giving of Torah
Fifty days after the first Pesach — Sinai.
Israel left Egypt at Pesach. Fifty days later, by careful count in Shemot 19, they stood at Mount Sinai while YHWH descended in fire. The ten commandments were spoken. The Torah was given. The covenant was cut. Shavuot.
The same day, in the same season, fifteen centuries later, fire fell again — and this time it landed on people, not stone.
Yeshua in Shavuot
The Ruach HaKodesh, on the same day, with the same fire.
What the Institutional Church Did
Renamed it Pentecost. Detached it from Sinai. Lost the count.
The institutional church kept the Greek name Pentecost but lost the Hebrew root. It dropped the counting of the omer (the fifty days from Firstfruits to Shavuot). It severed the link between the giving of Torah and the giving of the Ruach. Most Christians have no idea their Pentecost lands on the same calendar day Israel received the mitzvot at Sinai. The connection was hidden.