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. The next day after the seventh Shabbat you shall count fifty days… Vayikra 23:15–16 · KWS
The Torah Mitzvah
Fifty days counted from First Fruits. Two loaves of leavened bread waved.
Shavuot — Hebrew for "weeks" — is timed off First Fruits. 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 first fruits 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.
Centuries later He promised to give it again, on a different surface.
“But this is the covenant that I will make with the house of Israel after those days,” says YHWH: “I will put my law in their inward parts, and I will write it in their heart. I will be their Elohim, and they shall be my people.” Yirmeyahu 31:33 · KWS
Yeshua in Shavuot
The Ruach HaKodesh, and the Torah written within.
John the Immerser had said it at the Jordan, before Yeshua had taught a word: He will immerse you in the Ruach HaKodesh. Mattityahu 3:11 Yeshua Himself made it a promise with a condition, and the condition was His going: It is to your advantage that I go away; for if I don’t go away, the Counsellor won’t come to you. But if I go, I will send him to you. Yochanan 16:7 He named who was coming — the Counsellor, the Ruach HaKodesh, whom the Father will send in my name… Yochanan 14:26 — and how long He would stay: that he may be with you forever Yochanan 14:16. Risen, He gave what He had promised: he breathed on them, and said to them, “Receive the Ruach HaKodesh!” Yochanan 20:22
What arrived was the thing the prophets had been describing for centuries, and they described it as an inside job. I will put my Ruach within you, and cause you to walk in my statutes. You will keep my ordinances and do them. Yechezkel 36:27 Not a different set of instructions — His statutes, His ordinances, the same ones spoken at the mountain. What changed was where they are kept. The stony heart comes out; a heart of flesh goes in Yechezkel 36:26. Torah moves from tablets to inward parts, exactly as Yirmeyahu said it would.
That is why Shavuot is one moed and not two. Sinai: Torah given in fire, on stone, to a people just brought out. Shavuot fulfilled: the same Torah written on hearts, in a people just redeemed. I will put my laws into their mind; I will also write them on their heart. I will be their Elohim, and they will be my people. Ivrim 8:10 The covenant was never replaced. It was relocated — off the stone and into the person, so that obedience stopped being something read and became something carried.
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 First Fruits to Shavuot). Most who keep it have no idea Pentecost lands on the same calendar day Israel received the mitzvot at Sinai. The connection was hidden.