When God named the descendants of Abraham His children, He instructed them to rest on the 7th day(Exodus 20:8, The Ten Commandments), which would later be recognized as our modern Saturday (from sundown Friday to sundown Saturday).
Then God changed the plan and when Christ, His Son, rose from the dead, it was a Sunday. Christians, in later history, celebrated His Resurrection each Sunday as the "new" Sabbath.
Modern day Jews still celebrate the Sabbath on Saturday, while Christians celebrate on Sunday. Changes were made and accepted worldwide, just as the Gregorian Calendar (and others before that) was based upon the year of Christ's birth. That too is accepted worldwide, though the Jews use both their calendar and the Gregorian calendar.
When Christ rode into Jerusalem, the Jews were celebrating Passover. There were many Jews there who would not otherwise have been there due to this celebration. They were unwittingly spectators of his crucifixtion and then were witnesses who heard about His Resurrection.
Jews today still celebrate Passover, but Christians celebrate that time as Easter week, and Sunday as a celebration of His Resurrection, Easter Day.
Changes were made from the Old Testament ways of celebrating, to New Testament ways of celebrating the New Promises from God, as given by Christ Jesus.
Christ ascended into Heaven 40 days after Passover. The Apostles were told to wait in Jerusalem until the power of the Holy Spirit came to them. They waited 10 days, which must have seemed an eternity to them, and they didn't really know what to expect. The day the Holy Spirit came to them, thousands of people above the normal number of citizens, were in Jerusalem to celebrate yet another Jewish festival. Pentecost was a harvest festival that was celebrated 50 days after Passover. With the new power given to them, the apostles went into the streets of Jerusalem to proclaim the miracle they were experiencing. People noted that they were just fishermen, Galileans, yet they could speak all the different languages of all the thousands of people gathered to hear what they were saying. It was a day of miracles and 3000 converts to Christianity were made that day.
Jews still celebrate Pentecost as a harvest festival. Christians still call it Pentecost, but they celebrate the Harvesting of sinners into God's Kingdom.
Changes in celebrations, brought about by God's hand on many lives!
Has His hand changed YOUR celebrations of life yet???