B] The Truth of the Early Church.

In the Old Testament, there is the Feast of Firstfruits when the Israelites brought to the priest a sheaf of the first grain (fruit) they harvested and the priest presented it to God as a wave offering on the day after the Sabbath (on Sunday) following the Feast of Unleavened Bread.
Until they gave the offering of the firstfruits to God, they could not eat grain from the new crop(Leviticus 23).

The prophecy of this feast was fulfilled by Jesus: After celebrating the Passover Supper, Jesus was crucified on the cross at the Feast of Unleavened Bread-the day after the Passover, and He rose from death on the day following the Sabbath (Mt 16:9). By resurrecting as the firstfruits of those who had fallen asleep, Jesus fulfilled the prophecy concerning the first grain-the offering of the Feast of Firstfruits in the Old Testament (Mt 27:50-53; 1 Co 15:20).

According to these Bible-based teachings, the Early Church kept the Passover on the 14th day of the first month in the sacred calendar, celebrated the Feast of Unleavened Bread by fasting on the 15th day of the same month, and observed Resurrection Day to commemorate the resurrection of Christ.