The Hebrew word Shavuot means Weeks. It is the Festival of seven Weeks after the Passover. It is a God-Commanded festival of memorial, marking when God brought down the Covenant from Mount Sinai. Jesus was executed during an 8-day Passover Festival, as the Paschal Lamb. He rose on a Sabbath at the end of the Passover Festival and was found out of the tomb on Sunday morning. He ascended on the 49th day in the counting of weeks (seven weeks), as Shavuot was about to begin. He ascended on a Sabbath, just as he was raised on a sabbath. His disciples became Apostles as the First Fruits [timed fifty days, beginning at Passover] deemed ripe by God to go into ministry.
No offense, but I don't know where you're getting your faulty information from.
Firstly, the countdown to Pentecost begins on the day after the Feast of Firstfruits:
Leviticus chapter 23
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10] Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of
the firstfruits of your harvest unto the priest:
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11] And he shall wave the sheaf before the LORD, to be accepted for you:
on the morrow after the sabbath the priest shall wave it.
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12] And ye shall offer that day when ye wave the sheaf an he lamb without blemish of the first year for a burnt offering unto the LORD.
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13] And the meat offering thereof shall be two tenth deals of fine flour mingled with oil, an offering made by fire unto the LORD for a sweet savour: and the drink offering thereof shall be of wine, the fourth part of an hin.
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14] And ye shall eat neither bread, nor parched corn, nor green ears, until the selfsame day that ye have brought an offering unto your God: it shall be a statute for ever throughout your generations in all your dwellings.
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15]
And ye shall count unto you from the morrow after the sabbath, from the day that ye brought the sheaf of the wave offering; seven sabbaths shall be complete:
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16]
Even unto the morrow after the seventh sabbath shall ye number fifty days; and ye shall offer a new meat offering unto the LORD.
Secondly, Jesus was not raised from the dead on the sabbath.
Instead, even as we just read (vss. 10-11), the sheaf of the firstfruits was waved "on the morrow AFTER THE SABBATH", and not on the sabbath.
Furthermore, Paul twice referred to Jesus as "the firstfruits" in his first epistle to the Corinthians because Jesus was raised from the dead on the Feast of Firstfruits which, again, occurred on "the morrow after the sabbath", and not on the sabbath.
I Corinthians chapter 15
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20] But now is Christ risen from the dead,
and become the firstfruits of them that slept.
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21] For since by man came death, by man came also the resurrection of the dead.
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22] For as in Adam all die, even so in Christ shall all be made alive.
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23] But every man in his own order:
Christ the firstfruits; afterward they that are Christ's at his coming.
Further still, all 4 gospels record that Jesus resurrected the day after the sabbath, so, again, I don't know where you're getting your faulty information from.
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In the end of the sabbath, as it began to dawn toward the first day of the week, came Mary Magdalene and the other Mary to see the sepulchre." (Matt. 28:1)
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And when the sabbath was past, Mary Magdalene, and Mary the mother of James, and Salome, had bought sweet spices, that they might come and anoint him.
And very early in the morning the first day of the week, they came unto the sepulchre at the rising of the sun." (Mark 16:1-2)
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Now upon the first day of the week, very early in the morning, they came unto the sepulchre, bringing the spices which they had prepared, and certain others with them." (Luke 24:1)
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The first day of the week cometh Mary Magdalene early, when it was yet dark, unto the sepulchre, and seeth the stone taken away from the sepulchre." (John 20:1)
Lastly, seeing how Jesus truly rose "on the morrow AFTER THE SABBATH", or on "the first day of the week", or on what we would call Sunday, if we count 50 days forward from there, even as Moses instructed the children of Israel to do in Leviticus 23:16, then we realize that Jesus most definitely did NOT "ascend on a sabbath" as you erroneously claimed, but rather on the second day of the week or on what we would call Monday.