Why do some Christians keep the biblical festivals that most of mainstream Christianity patently rejects? Most churches celebrate Easter and Christmas, although the Bible and the example of the apostles and early Church show that we should observe other annual days of worship.
The correlation between the harvest festivals Jesus observed and what He has already done or will do to harvest the sons and daughters of God is made clear in the Scriptures. The first three festivals, representing what He has already done, are undeniably linked to Him. Once we see that pattern established, the significance of the remaining festivals becomes obvious. They continue to reveal God's great purpose and plan for the salvation of mankind.
The Bible and other historical records of the apostolic era confirm that the original Christian Church continued to observe the same festivals Jesus observed. In regard to the Passover and Days of Unleavened Bread, the apostle Paul wrote to the congregation in Corinth, "Get rid of the old yeast that you may be a new batch without yeast-as you really are. For Christ, our Passover lamb, has been sacrificed. Therefore let us keep the Festival, not with the old yeast, the yeast of malice and wickedness, but with bread without yeast, the bread of sincerity and truth" (1 Corinthians 5:7-8 1 Corinthians 5:7-8  Purge out therefore the old leaven, that you may be a new lump, as you are unleavened. For even Christ our passover is sacrificed for us:
 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
American King James Version×, New International Version).
Paul here instructed the Corinthians, a predominantly gentile congregation, to keep the Feast of Unleavened Bread with a renewed understanding of its relationship to Christ and the sincerity of their confidence in the truths they had learned.
On another occasion we are told that Paul "was hurrying to be at Jerusalem, if possible, on the Day of Pentecost" (Acts 20:16 Acts 20:16For Paul had determined to sail by Ephesus, because he would not spend the time in Asia: for he hurried, if it were possible for him, to be at Jerusalem the day of Pentecost.
American King James Version×). We have already seen that Christ's disciples were all in Jerusalem observing Pentecost when God gave them the Holy Spirit, thus founding the New Testament Church (Acts 2:1 Acts 2:1And when the day of Pentecost was fully come, they were all with one accord in one place.
American King James Version×, 4). No indication is to be seen in the New Testament that the apostles or their converts ever observed any religious celebrations except those that Jesus Christ Himself observed.
The practice of observing these festivals was preserved well into the fourth century. However, in 325 a significant debate over the Passover, known in history as the Quartodeciman controversy, erupted. Because of the intense anti-Semitic sentiment of that era, the Council of Nicea agreed to abandon the observance of the Passover because of its association in people's minds with the Jews. That decision was met with fierce opposition from congregations and church leaders from the eastern portion of the Roman Empire. They vigorously resisted abandoning the example and practice of Jesus and the apostles.
Eusebius, an early church historian, recorded their reaction. "But the bishops in Asia were led by Polycrates in persisting that it was necessary to keep the custom which had been handed down to them of old. Polycrates himself in a document which he addressed to Victor and the church of Rome expounds the tradition which had come to him as follows. 'Therefore we keep the day undeviatingly, neither adding nor taking away, for in Asia great luminaries sleep, and they will rise on the day of the coming of the Lord, when he shall come with glory from heaven and seek out all the saints. Such were Philip of the twelve apostles . . . There is also John, who lay on the Lord's breast . . . , and there is also Polycarp . . . All these kept the fourteenth day of the Passover according to the gospel, never swerving, but following according to the rule of the faith'" (Eusebius, The Ecclesiastical History, English translation from the original Greek by Kirsopp Lake, Vol. II, G.P. Putnam's Sons, New York, 1926, pp. 505, 507).
Unfortunately, by abandoning the festivals Jesus observed and eventually turning to pagan celebrations such as Easter and Christmas, the majority of professing Christians lost an important part of their heritage. Lost, at the same time, was the wonderful understanding of how God will harvest all mankind, bringing His sons and daughters into His Kingdom and sharing with them the wonderful gift of eternal life.