The Feast of Shavuot, or the "Feast of Weeks or Sabbaths," is also known as "the Season of the Giving of the Law" and “Fiftieth”.  It originated during the time of the Exodus from Egypt and was first celebrated 50 days after their departure from Egypt. 

They arrived at Mt Sinai on this day, where they received the God’s Instructions, written by Moses on two tablets of stone, during his meeting with GOD on the Mount.

The Rabbis could prove that Shavuot was the day that the Torah was given to Moses on Mt Sinai
Here Is How:

Nissan15 Days
Iyyar30 Days = 45 Days
1st of Sivan – At Mt Sinai – Moses goes up the mountain, comes back down and tells the people about the Covenant (Exodus 19:7) = 1 day
2nd of Sivan (Exodus 19:8) – Moses goes back up the mountain, tells God that Israel accepts the Covenant = 1 Day
When he comes down, Moses tells the people they have 3 days to prepare to meet God. This time covers Sivan 3-5
The giving of the Torah time = 45 + 5 = 50 Days
The end of the 50-day count of the Omer is Shavuot (Pentecost)

It was also the giving of the Roush Hakodesh (Holy Spirit) in Acts 2
What is the function of the Ruach Hakodesh?

Let’s Look at scripture:
In Genesis 41:38 - He is the origin of supernatural abilities
In Exodus 31:2-5 - He is the giver of artistic skills
In Judges 3:9-10 - He is the source of power and strength
In 1 Samuel 19:20,23 - He is the inspiration of Prophecy
In Micah 3:8 - He is the mediator of God’s messages
In Ezekiel 36:25-29 - He cleanses the heart for holy living
In John 16:8-11 - He brings conviction
In John 14:17 and Romans 8:9-11 - He completely indwells the Believer
In John 14:26,16:13, and 1 Corinthians 2:13-15 - He imparts spiritual truth
In John 16:14 - He glorifies Yeshua
In Acts 1:8 - He endows us with the power to proclaim the gospel
In I Corinthians 12:4-11 - He imparts gifts for ministry
In 2 Thessalonians 2:13 - He sanctifies the Believer

Scriptures have never associated Shavuot with Sinai.
The idea of the giving of the Torah and the birthday of Judaism quickly was accepted as recorded in ancient Jewish literature (Shabbat 86a and Jubilees 6:19)

This is how modern Shavuot became known as “the Giving of the Law.”
This also produced another custom.
• It is staying up all night studying the Torah
• One of the Books studied on Shavuot is the Book of Ruth

There are 7 Major Theological Themes of Ruth
At least seven major theological themes emerge from the book of Ruth.
• Each theme shows the value of a woman

First, Ruth the Moabitess illustrates that God's redemptive plan extended beyond the Jews to Gentiles, including Gentile women (Ruth 2:12).

Second, Ruth demonstrates that women are co-heirs with men of God's salvation grace (I Peter 3:7).

Third, Ruth portrays the virtuous woman of Proverbs. 31:10 (see Ruth 3:11).

Fourth, Ruth describes God's sovereign care (Ruth 1:6, 4:13) and providential care (Ruth 2:3) of seemingly unimportant people at insignificant times, which later prove to be crucial to accomplishing God's will.
• Ruth because part of God’s plan

Fifth, Ruth along with Tamar (Genesis 38), Rahab (Joshua 2) and Bathsheba (II Samuel 11-12) stand in the genealogy of the Messianic line (Ruth 4:17, 22; see also Matthew 1:5).

Sixth, Boaz, as a type of the Messiah, becomes Ruth's kinsman-redeemer (Ruth 4:1-12).

Seventh, David's right (and thus the Messiah's right) to the throne of Israel is traced back to Judah (Ruth 4:18-22; see also Genesis 49:8-12).
• David would not have existed without Ruth.

Consider this: The story of the Messiah’s genealogy through Ruth and Boaz does not begin with the book of Ruth.

It begins in the Book of Judges with Rahab the Harlot (Inn Keeper)
• It is an example of a word changing through age (Example: Gay – Changed from “happy” to a vastly different meaning)
The first part of Rahab—“Ra,” was the name of the Egyptian sun god.
As an Amorite, Rahab belonged to an idolatrous people.

Some of the ancient sages said that she became the wife of Joshua, but in the royal genealogy of Yeshua, Rahab is referred to as being the wife of Salmon, one of the two spies she sheltered.
• In turn, she became the mother of Boaz, who married Ruth.

Rahab, the one-time heathen harlot/ innkeeper, married into one of the leading families of Israel and became an ancestress of our Lord.
• She is the only woman, by name, listed in the faith chapter of Hebrews 11.

While her name came to be sanctified, Hebrews (Hebrews 11:31) and James (James 2:25) still labeled her as Rahab the harlot.
• She still carried the evil name and title, thus declaring the unique grace of the transforming power of God.

As a foreigner, she honored Romans 10:9-10. She believed with her heart, confessed with her mouth, and acted on her profession of faith at the risk of her life.

Rahab is a fitting illustration of another miracle of God’s divine grace; the calling forth of His congregation out of a godless, gentile world

Scripture has two genealogies of Yeshua.
The first genealogy in Luke 3:32 reads "who was the son of Jesse, who was the son of Obed, who was the son of Boaz, who was the son of Salmon, who was the son of Na-as-son,"
The second is written in Matthew 1:5 –6,Salmon begat Boaz of Rachab ((KJ) Rahab (ASV)); Boaz begat Obed of Ruth; Obed begat Jesse; Jesse begat David the king…

What does this mean?
It means that the mother of Boaz was Rahab the harlot of Jericho.
What was the name of Obed’s mother?
• It was Ruth, from Moab.

Without these two women, David would never have been born.
• Rahab, the harlot, was David's great, great grandmother.
• Ruth, from Moab, was David's great grandmother.

The Moabites were pagans, occasionally offering human sacrifices to idol-gods.
As a result, God prohibited the Jews from intermingling and intermarrying with Moabites (Ezra 9:10-12) —unless a Moabite renounced all that being a Moabite meant and became all that it meant to be a Jew.
• Ruth is a Moabite, a descendant of Moab.
Boaz, who became Ruth’s redeemer-husband, was the son of Rahab. (Ruth 4:21, 1 Chronicles 2:11, Matthew 1:5)

Imagine the stories Boaz heard as he grew up.
He had a mother who had been a foreigner and a harlot; yet was grafted into the olive tree of Israel by the grace of God.

This affected the way Boaz viewed Ruth that day he saw her gleaning in his field.
Other men might have simply seen a foreign woman scrounging for food, like a parasite.

But Boaz saw something familiar and dear in a woman who had left her family, her nation, and her gods, to embrace Naomi, her nation, and her God.
• He was raised in it.

If the Messiah who is to redeem the whole world from what is evil in the world and make it work for good is to come from the house of David, then not only Jews but non-Jews must enter David's line and contribute to redemption that enters Messiah's birthright and inheritance.

It is not Ruth, a Moabite idolater, but Ruth who says "Your God will be my God" who becomes the great-grandmother of David.

Boaz was uniquely prepared by God for Ruth and Ruth for Boaz.
• It was a marriage made in heaven. (Jew and Gentile).
Their union produced a son named Obed, who had a son named Jesse, who had a son named David, who became the greatest king Israel ever had.
That is until David’s generational line produced a King named Yeshua.
God is weaving his grace throughout the Bible—even though the genealogies!

One of the canonical books of the Tanakh (Old Testament) being named after a Moabite woman is itself a testimony that a miracle of God’s grace had taken place.  

The Spiritual Applications
Consider these questions:
Why do we need to keep this count through seven weeks?
Torah assigns all of the other festivals a specific month and day, so why not Shavuot?

Allow me to give you five reasons:
1) The annual count reminds us not to take Shavuot for granted.
It was not known that once Israel was freed from Egypt, the gift of God's Word at Mount Sinai would be given. This was another sign of divine intervention in human affairs.

2) We count the days to prepare ourselves for a new encounter with the God who liberated us from bondage.
As followers of the Messiah, we can re-enact these events with special zeal.

By remembering the connection between Yeshua's resurrection at Pesach and the outpouring of the Spirit at Shavuot 49 days later
* Because Shavuot (Pentecost) culminates with the counting of the Omer for 50 days it is called the Atzeret or conclusion to Passover (Pesach).

3) The believers in the Messiah Yeshua are on a journey out of Egypt (a type of the world's system and its evil ways) in the wilderness (of life), waiting our time to meet God face to face on Mount Sinai (Exodus [Shemot] 3:12).
* At our Mount Sinai (spiritually), God will forever reveal Himself to us in a new and greater way

4) For all believers in the Messiah Yeshua, the Torah that was given at Mount Sinai represents the Word of God, the entire Bible.
The believer in Yeshua spiritually experiences Shavuot (Pentecost) when the Holy Spirit of God (Ruach Hakodesh) reveals the Word of God to him in a deeper and more powerful way.
• His understanding and desire for the Bible increase accordingly.

5) Preparing to Meet God

The Applications
A sheaf in the Bible is used to typify a person or persons (Genesis [Bereishit] 37:5-11).
Yeshua will return to earth (Zechariah 14:4) during His second coming as King over all the earth.
• He also will bring the sheaves (the believers in Yeshua as the Messiah) with Him
(Psalm (Tehillim) 126; Jeremiah (Yermiyahu) 31:9-14; Joel 3:11-13; Zechariah 14:3-5; Matthew [Mattityahu] 13:37-39; Mark 4:26-29; Hebrews 12:1; Jude 14; Revelation 1:7).

The 144,000 Jewish witnesses who witness of Yeshua during the birth pains of the Messiah (also known as the tribulation) are firstfruits to God during the tribulation
Revelation 14:1-4 reads, “Then I looked, and behold, on Mount Zion stood the Lamb, and with him 144,000 who had his name and his Father's name written on their foreheads. And I heard a voice from heaven like the roar of many waters and like the sound of loud thunder. The voice I heard was like the sound of harpists playing on their harps, and they were singing a new song before the throne and before the four living creatures and before the elders. No one could learn that song except the 144,000 who had been redeemed from the earth.  It is these who have not defiled themselves with women, for they are virgins. It is these who follow the Lamb wherever he goes. These have been redeemed from mankind as firstfruits for God and the Lamb,

 Every time a person receives Yeshua the Messiah as his own Lord and Savior, he spiritually experiences Passover (Pesach).
He is to flee Egypt (the world's evil system and ways) and trust (emunah) in the Messiah, the Lamb of God, and allow Yeshua to be the doorpost of his heart.

As believers, we are then to seek to live holy lives before God and experience Unleavened Bread (Hag HaMatzah).
Just as Yeshua arose from the dead, we are to consider our former ways dead to us and experience the newness of life in the Messiah

When we do this, we can be immersed (baptized) in the Holy Spirit (Ruach Hakodesh) and have the power of God (the anointing) in our lives.
At that time, God will begin to take us on a spiritual journey through the wilderness of life.

In the process of experiencing life's bitter disappointments and struggles, if we keep our eyes upon God, He will take us from Passover (Pesach) to Shavuot (Pentecost) where He will reveal His ways and His Word, the Bible, in a deeper and progressive way

By keeping our eyes on the Messiah through life's struggles, God will not only reveal His Word, the Bible, to us in a greater way, but He also will refine our faith like fine flour just as was done to the wheat.

If we put our entire trust (emunah) in Yeshua through our spiritual journey in the wilderness of life as God refines our faith and reveals Himself to us in a greater way, our spiritual journey will not end in the wilderness of life.
• God will take us forward to spiritually experience the fall festivals and our spiritual promised land

The fact that We will all be keeping the biblical calendar in the Messiah's Kingdom makes it clear that keeping the calendar is part of kingdom living.
• On that day, all mankind will keep the seventh-day, biblical Sabbath, and God’s Feasts.
When we sit down to eat with the Master, the only menu options will be kosher.

The final great move of God with His people will involve 2 items as recorded in Revelation 14:12. It reads “Here is the patience of the saints, who keep the commandments of God and the faith of Jesus (Yeshua)”.

Closing Scripture
In closing, I cannot think of a better scripture than Isaiah 35:8-10.
It reads, “And a highway shall be there, and a way, and it shall be called The way of holiness; the unclean shall not pass over it, but it shall be for the redeemed: the wayfaring men, yea fools, shall not err therein.  No lion shall be there, nor shall any ravenous beast go up thereon; they shall not be found there, but the redeemed shall walk there: and the ransomed of YHVH shall return and come with singing unto Zion, and everlasting joy shall be upon their heads: they shall obtain gladness and joy, and sorrow and sighing shall flee away.