Feast of Weeks (Shavuot):
The Feast of Weeks/Shavuot is celebrated during the May/June timeframe. Exodus 34:22 tells us: "Observe the festival of Shavuot with the first-gathered produce of the wheat harvest, and the festival of ingathering at the turn of the year...."
Torah directs the seven-week Counting of the Omer (which begins on the second day of Passover and culminates after seven weeks, the next day being Shavuot). The counting of the days and weeks conveys anticipation of and desire for the Giving of the Torah. In other words, at Passover, the Israelites were freed from their lives of slavery in Egypt; and 50 days later on Shavuot they accepted YHWH's Torah which made them a nation committed to serving God.
This Feast was fulfilled by the coming of the promised Ruach HaKodesh (Holy Spirit) on the disciples of Yeshua in the Temple. It represents the beginning of the body of Messiah on Earth, in which ALL believers, redeemed through the blood of Messiah, are lifted up before ADONAI and set apart as holy (Acts 2, John 14:15-18, Ephesians 2:11-22 and the Book of Ruth). During Shavuot we not only read the Book of Ruth, but also Exodus 19:1 thru 20:23; Numbers 28:26-31 and Ezekiel 1:1-28, 3:12.
Among the awesome readings for Shavuot are passages such as Acts 2 which, when examined in context are absolutely mind-blowing:
Acts 2: 21. And it will be (that) all who call (on) the name of Master YHWH will be saved.
Acts 2: 32. This Y'shua Elohim raised, and we (are) all of his witnesses. 33. And this is he who is exalted at the right hand of Elohim, and received the promise from the Father concerning the Ruach haKodesh. And he has poured out this gift, which behold you see and you hear. 34. For it was not (that) Dawid did ascend into Heaven, because he said, Master YHWH said to my Master, sit (yourself) at my right hand. 35. Until I place your enemies (as) a footstool for your feet.  36. Truly, therefore, let all the house of Israel know that Elohim has made this Y'shua the Mashiyach whom you executed on a stake both Master YHWH and Mashiyach." 37. And when they heard these things they were touched in their hearts, and they said to Shimon and to the rest of the Shlichim, "What should we do, our brothers?" 38. Shimon said to them, "Repent and be immersed each of you in the name of Master YHWH-Y'shua for the forgiveness of sins, that you may receive the gift of the Ruach haKodesh.
 Psalm 110:1.
 "Has made" meaning from Y'shua's birth; one of the clearest statements in the NT that Y'shua had occurrences of human and divine natures co-existing within him. The human side's total obedience to YHWH contributed to Y'shua qualifying as haMashiyach; the fact that the Ruach haKodesh (another name for YHWH), dwelled inside Y'shua, also establishes Y'shua as the image of YHWH.
 Shimon was preaching from the steps of the Temple in Jerusalem. Just below him were hundreds of mikveh (immersion) baths. Both the steps he spoke from and the baths are visible today outside the Western Wall. In Peter's day baptism wasn't an act of conversion from one religion to another, but an act of purification from sin. A person repented of their sin, prayed, and then entered into the waters of the mikveh to symbolize atonement.
 MarYah and Y'shua appear next to one another! Therefore, Keefa is saying that the divine part of Y'shua and YHWH are one and the same; he is referring to Him in both ways.
Further explanation: Within Y'shua the man is an occurrence of the One Divine Nature of YHWH, also known as the Ruach haKodesh. This is the literal meaning of the fullness of YHWH dwelling inside Mashiyach, and in accordance with Tanakh prophecy (Isaiah 53:1, Zechariah 12:10). The divine and human natures exist separately yet side-by-side within Y'shua. When it says He "sits at the right hand of His Father" it doesn't necessarily mean "sit" as in a separate chair. YHWH, who is Spirit, doesn't "sit." To be at the right hand (side) was to be on the side of power and favor in Hebraic thought, especially with respect to YHWH.
The following is a further explanation about the celebration of Shavuot by Rabbi Brian Tice (Acting Rosh Yeshiva and Semikha Examiner, and Professor of Jewish Studies and Languages at the Messianic Jewish Rabbinate).
On Shavuot (aka Firstfruits), usual Sabbath prohibitions are in effect. We celebrate by staying up all night long studying Torah, since it is the anniversary of Israel receiving the Torah on Har Sinai, starting from D'varim 16. A requirement from the written portion of the Torah is to wave (and then eat) loaves of leavened bread with wine as the closing bookend to the Feast of Matzo (commanded in Wayyiqra 23:17).
Another ancient ruling calls for the eating of dairy products - cheese, blintzes, bourekas, etc., because milk represents the giving of life and nourishing that life (and spring was the only season when cheese was produced in ancient times).
At the first Shavuot, when the Jewish people received the Torah at Har Sinai, included with this was the special instructions for how to slaughter and prepare meat for eating (part of the Oral Torah). Until then, we had not followed these laws.The new kosher slaughter procedure rendered all their meat and cooking vessels treif ("not kosher"). The only alternative was to eat dairy, which requires no advance preparation.
In the 1st Century, prior to 70 CE, it was known as Atzeret (solemn assembly) because a pilgrimage to the Jerusalem Temple was required. It later became customary to wear white on this day because it is the date on which Israel became the bride of Hashem through our acceptance of His Covenant (Torah).