My current trajectory as a reformed Baptist who adheres to the 1689 London Baptist Confession of Faith began in 2009. As I studied the reformed faith, I also found the Regulative Principle of Worship, which states that the ordinances of worship are found only in the Bible and that man is not to add or detract from the word of God. In 2011 it became apparent that Christmas was more about the world and not at all about Christ when many churches canceled their Sunday services because Christmas fell on the Lord's Day. Celebrations such as Christmas and Easter are not commanded, nor prescribed, in the Bible; therefore, my family and I no longer celebrate these holidays.
Our conviction in this area does not imply that all Christians should do the same or that we think differently of other Christians because they continue to celebrate these holidays. We celebrate the Lord's birth, death, and resurrection every Sunday when we meet to worship God in His house; so for us, there's no need to single out special days of worship.
As I continue to read the Puritans, I find that many of them upheld the Regulative Principle of Worship as well. Let's look at an exposition of Hosea 5:5 from An Exposition of the Prophecy of Hosea by Jeremiah Burroughs (edited for length):
"Ver. 5. And the pride of Israel doth testify to his face: therefore shall Israel and Ephraim fall in their iniquity; Judah also shall fall with them.Obs. 1. Ignorance and pride usually go together.Obs. 2. Idolaters are proud men, and idolatry is a proud sin.1. Idolaters regard the true worship of God as a mean thing, as a thing beneath them.2. They presume to put more dignity on a creature than God has, to put more honour on places than God and nature has imposed.3. They prescribe the form of God's worship. The worship of God is the dearest thing he has in the world; and for any creature to take upon him to prescribe which way he shall be worshipped, is the most notorious pride in the world.4. They honour what is a man's own because it is his own, rather than what is God's. Do not you see it plainly in all superstitious, idolatrous people? As in that one thing of days? God has set one day apart for the honouring of himself, and for the celebration of the birth, death, resurrection, and ascension of Jesus Christ, and of the whole work of our redemption: how is that day slighted and neglected! But what a horrible wickedness is it accounted not to keep that which man sets apart by himself, that day which is of man's appointment! Men will set apart a day for the honour of Christ, and insist that Christ is quite forgotten if that day be forgotten, and Christ is much dishonoured if that day be not regarded. I appeal to you, who sets it apart? whose is it? Is it God's, or is it yours? God's? Certainly, if such a thing were so acceptable to God as men conceive it to be, we should have some little hint, somewhat in the book of God regarding it."
***"And he [Jesus] said unto them, Full well ye reject the commandment of God, that ye may keep your own tradition," (Mark 7:9).