Why are Christians not celebrating God's festivals?

Do it, and tell others. That is how you change people's behavior and encourage consistency with scripture. Very few Christians read the bible, or ever have for that matter, so they don't actually know what's in it and what isn't.

Because in Paul's letters to the churches in Asia Minor, he tells the Gentile believers that there is no need for them to celebrate the Jewish Festivals in order to be Christians. This is what the gnostics and the Judaizers were trying to do: tell people that to be saved, they had to accept Jesus Christ AND abide under all the legal requirements of Mosaic law, such as the festivals, eating kosher and the circumcision. Paul said in many different passages, in many different ways that it is not necessary. Jesus Christ and Him only is what saves from sin.   Jesus Christ fulfilled all the symbolism of Pesach and the other Jewish religious rites and festivals. We celebrate Him in new ways--like Communion. The fellowship of believers and the breaking of bread is the only rite Christians are commanded to partake of. However, for modern Christians who find meaning in celebrating Jesus' birth at Christmas, His crucifixion and resurrection at Easter, and his Ascencion and gift of the Holy Spirit at Pentecost, there need be no shame. We can be aware of the pagan elements that have crept in, and still worship Him in full sincerity in our hearts, and find meaning in these festivals, rituals and symbolic acts. It is the Love of Christ in our hearts, and the Spirit that testifies within us, that gives meaning to these holidays--not the modern secular world's twisted view of them.   Bless.

Easter does not have a pagan background. It's assumed to be pagan because of the name, but the name is perfectly Christian in other languages. Christmas isn't pagan just because some of its customs are of pagan origin. Celebrating the Birth of Jesus Christ is hardly a pagan custom. We don't celebrate the feasts of the Mosaic Covenant because Christ's sacrifice did everything the Mosaic Covenant was supposed to do, and then some. So Christ's sacrifice made the Covenant obsolete.

Because, when Christians were killing the pagans, the Roman emperor, Constantine, was a pagan too, but he changed some rites and festivals' dates. Constantine have done it, because he was smart and thinked, that changing some little things won't make any difference. Christ was born in March, but we celebrate his born at December, the pagans' god, the Sol Invictus. And, at Saturday, the Sixth day, God rested, so, the Christians had to make the Saturday an Holy Day. But Constantine changed it to Sunday, because it's the Holy Day for pagans.