Deu 16:16 "Three times a year all your males shall appear before the Lord your God in the place which He chooses: at the Feast of Unleavened Bread, at the Feast of Weeks, and at the Feast of Tabernacles; and they shall not appear before the Lord empty-handed.
Note - the destruction of the temple of God in Jerusalem in 70AD ended all Jewish feasts and Judaism.
Christians must not keep any Jewish feast for our Lord Jesus had fulfilled all of them.
Heb 8:13 In that He says, "A new covenant," He has made the first obsolete. Now what is becoming obsolete and growing old is ready to vanish away.
1. Feast of Unleavened Bread
After our Lord Jesus was crucified as the Passover Lamb, Christians must abide in His Word the Bread of life fulfilling the Feast of Weeks.
2. Feast of Weeks
On the third day our Lord Jesus became the firstfruits of resurrection. The outpouring of the Holy Spirit on Pentecost and the subsequent harvest of three thousand souls fulfilled Feast of Weeks.
3. Feast of Tabernacles
Immediately after the resurrection of our Lord, He breathed the Holy Spirit into His Apostles and making their physical bodies to become tabetnacles (temples) of God thus fulfilling the Feast of Tabernacles.
Devout Jews saved at Pentecost
Act 2:5, 37, 41 And there were dwelling in Jerusalem Jews, devout men, from every nation under heaven.... Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, "Men and brethren, what shall we do?".... Then those who gladly received his word were baptized; and that day about three thousand souls were added to them.
After the veil in the temple was torn, God departed from the temple. When the devout Jews from foreign lands came to keep the Feast of Pentecost, they were converted to Christianity by the power of the Holy Spirit and 3000 Jews believed Jesus and were baptized in Acts 2.
This fulfilled the words of our Lord Jesus that devout Jews who believe Moses will also believe and accept Jesus as their Messiah. These new Christians then took the gospel back to their synagogues in foreign lands to convert the Jews there.
Paul's Evangelism at Feasts
Act 18:20-21 When they asked him to stay a longer time with them, he did not consent, but took leave of them, saying, "I must by all means keep this coming feast in Jerusalem; but I will return again to you, God willing." And he sailed from Ephesus.
God gave the Israeli Christians almost 40 years to evangelise the Jews before the destruction of the temple of God. Paul and the other Apostles frequently returned to Jerusalem for the various feasts so that they could evangelize and convert more devout Jews from foreign lands.
Jews sent to Exile Again
After the destruction of Jerusalem and the temple of God, the Jews were once again scattered throughout the world. In their new foster countries, they could be saved in communities, churches and even some synagogues, where the gospel was shared.
John 5:46-47 "For if you believed Moses, you would believe Me; for he wrote about Me. But if you do not believe his writings, how will you believe My words?"
Devout Jews who believed Moses will be saved for they will also believe in Jesus as the Christ.
The Priesthood and Jewish leaders then were hypocrites, so they rejected and crucified our Lord Jesus.
Similarly, the Jews in Israel today are blind hypocrites, atheists and agnostics, otherwise they are already Christians.