Regarding the feasts of the Lord, it is very instructive to study the history of the first 30 years of the Christian Church recorded in Scripture. What Holy Days did they keep? It's surprising how many of "the feasts of the Lord" are found in the book of Acts.

The first mention of God's feasts in the book of Acts is found in 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×: "When the Day of Pentecost had fully come, they were all with one accord in one place." This day of Pentecost is one of God's feasts found in Scripture.

Then in Acts 12, two of "the feasts of the Lord" are mentioned—the Passover and the Days of Unleavened Bread (Acts 12:3-4 Acts 12:3-4 [3] And because he saw it pleased the Jews, he proceeded further to take Peter also. (Then were the days of unleavened bread.) [4] And when he had apprehended him, he put him in prison, and delivered him to four squads of soldiers to keep him; intending after Easter to bring him forth to the people.
American King James Version×). Peter was miraculously freed from his chains at that time, and the Church rejoiced over this liberation. Many would have remembered that during this day, the Israelites were also freed from their Egyptian bondage.

Later Luke, in describing his travels with Paul, mentions sailing after the Days of Unleavened Bread were over, showing they had stayed to observe them in Philippi before continuing their trip (Acts 20:6 Acts 20:6And we sailed away from Philippi after the days of unleavened bread, and came to them to Troas in five days; where we stayed seven days.
American King James Version×).

Moreover, Luke records Paul "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×). If these feasts were only for the Jews and abolished for Christians, they certainly would not have been mentioned as important for Paul and his party.

Finally, we see Luke mentioning another feast, the Day of Atonement, in their travels: "Now when much time had been spent, and sailing was now dangerous because the Fast was already over ..." (Acts 27:9 Acts 27:9Now when much time was spent, and when sailing was now dangerous, because the fast was now already past, Paul admonished them,
American King James Version×). "The Fast" is referring to the Day of Atonement, the only day in Scripture commanded by God to be observed with a fast (Leviticus 23:27 Leviticus 23:27Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation to you; and you shall afflict your souls, and offer an offering made by fire to the LORD.
American King James Version×).

So we find not an inkling in the book of Acts—a chronicle of the first 30 years of Church history—that the feast days had been changed or abolished, or other days substituted in their place. Rather, they assumed a much greater meaning to the Christian community. The Encyclopaedia Britannica confirms this, stating that "the first Christians ... continued to observe the Jewish festivals, though in a new spirit, as commemorations of events which those festivals had foreshadowed" (11th edition, vol. 8, p. 828).