All the Holy days are about the Christ. Some have been fulfilled, like Passover, and some have not. We are instructed by the Christ to continue to observe, in remembrance of this Shadow, even after it has been fulfilled. Remembering one while rejecting the others is not wise, IMO. I have yet to find where the "New Covenant" has anything to do with the annulment of God's laws, rather, How His Laws are administered, (He writes them on our heart) and how sins are forgiven. (His Blood) I can't find where the Christ teaches to reject God's definition of Holy, and replace it with man's definition of Holy. I don't believe it exists in the Bible, just the minds of religious man.
This same Christ, as the Word of God, also said to remember this.
8 Remember the sabbath day, to keep it holy.
9 Six days shalt thou labour, and do all thy work:
10 But the seventh day
is the sabbath of the LORD thy God:
in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that
is within thy gates:
The Holy Days of the Christ are not a huge celebration in Mainstream Christianity. Easter is. Christmas is, even Halloween. But not the Feasts the Christ calls "My Feasts", certainly not Feast of Unleavened bread or the rest.
While is it true that these "HOLY" Days of the Christ are a "shadow" of things to come, they are from the Christ. They are created by Him for us. He is the substance, they are about Him, that is why He said they would be here as long as heaven and earth are here.
In contrast, there are many High Days of Mainstream Christianity which are a shadow of nothing to come, and were not created by the Christ, but by religious man.
I believe the entire Bible warns and gives examples of listening to "Another Voice" besides the Word of God.
In my view Passover without Feast of Unleavened bread is like Faith without Works.