Oops. Sorry. Fault.
If you read very carefully, or actually not so carefully, you will see that Hebrews is speaking of a change from one system to another; from the Levitical Order of the sacrificial system to the Melchizedekian Order of Jesus Christ. "As He also says in another place: 'You are a priest forever According to the order of Melchizedek'" (Heb. 5:6). It was not a change of the Levitical Order. It was an abolishment of the Levitical Order.
The "holy days" were part and parcel of the Levitical system. Melchizadek never kept the festival days of Leviticus.
"But now He has obtained a more excellent ministry, inasmuch as He is also Mediator of a better covenant, which was established on better promises." (Heb. 8:6)
The imperfect Levitical system was completely replaced by the perfect one after the Order of Melchizedek.
Try again. Where is there an divinely authorized change to the Levitical system so that bloody festivals become unbloody. (I'll give you a hint, there is only one, and it is directly referenced in the establishment of the new covenant.)
Context, context!
The writer of the book called "to a group of Messianic Jews" or Hebrews is quoting Psalm 110:4
4 The LORD has sworn and will not change His mind, "Thou art a priest forever According to the order of Melchizedek."
b'shem Y'shua
NASBu Psalm 110:1 A Psalm of David. The LORD says to my Lord: "Sit at My right hand, Until I make Thine enemies a footstool for Thy feet."
2 The LORD will stretch forth Thy strong scepter from Zion, saying, "Rule in the midst of Thine enemies."
3 Thy people will volunteer freely in the day of Thy power; In holy array, from the womb of the dawn, Thy youth are to Thee as the dew.
4 The LORD has sworn and will not change His mind, "Thou art a priest forever According to the order of Melchizedek."
5 The Lord is at Thy right hand; He will shatter kings in the day of His wrath.
6 He will judge among the nations, He will fill them with corpses, He will shatter the chief men over a broad country.
7 He will drink from the brook by the wayside; Therefore He will lift up His head.
Completely agree.
The "holy days" were part and parcel of the Levitical system.
Not so. God's feast days fall outside of any covenant and here's why.
1. Passover, one of God's festivals, was established and inaugerated before the covenant was struck at Mt. Sinai. This occurs in Exodus chapter 12 and was not part of any covenant.
2. Jesus Christ always kept the holy days even though he routinely eschewed non-biblical Jewish traditions. BTW, this should be reason enough for any follower of Christ to keep the Lord's holy days.
3. Paul expressly says in scripture that the feast of unleavened bread is to be kept:
1Co 5:7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:
1Co 5:8 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.
4. God's Holy Days are prophesized to be kept in the future. For example, Zechariah prophesizes that after the day of the Lord:
Zec 14:16 And it shall come to pass, that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King, the LORD of hosts, and to keep the feast of tabernacles.
ALL nations. And what is the price of not keeping the feast of tabernacles in the future?
Zec 14:18 And if the family of Egypt go not up, and come not, that have no rain; there shall be the plague, wherewith the LORD will smite the heathen that come not up to keep the feast of tabernacles.
Zec 14:19 This shall be the punishment of Egypt, and the punishment of all nations that come not up to keep the feast of tabernacles.
Therefore the holy days are not part of any covenant, but instead are days that God created to help us understand and celebrate his plan of salvation.
Another interesting verse is Genesis 1:14
Gen 1:14 And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
The word translated "seasons" is the same hebrew word used in reference to God's feast days. It's the "set time" when we are to come before the Lord.