Holy days were for anybody who worshiped the god of Israel. The Gentiles didn't follow them of course but every Gentile did not become "Christian". Most remained pagan.
Historically, pagans (Gentiles) who became Christians did not have to keep the law. The circumcision issue that arose in the first century, was proof of this. Acts 15 relates the outcome of a decision made by the governing body in Jerusalem concerning the things that gentile brothers needed to do....
"and we ourselves have favored adding no further burden to you except these necessary things: to keep abstaining from things sacrificed to idols, from blood, from what is strangled, and from sexual immorality. If you carefully keep yourselves from these things, you will prosper. Good health to you! (Acts 15:28, 29) There was no mention of keeping the law, including the Sabbath or circumcision, which were very important to Jews, but not to Gentiles.
As history also demonstrates, pagans who became part of Christendom (in the later centuries) brought a lot of their former religious beliefs and customs with them, creating a fusion that is forbidden in scripture, both OT and NT. (Deut 18:9-12; 2 Cor 6;14-18)
Christians believe Christ's sacrifice abolished the old law. No doubt about that. That's what Christian's believe, it's not what everybody believes.
And isn't this what we all have to make our choices about?
What constitutes God's law for all of us regardless of what label we wear? It isn't what we choose to believe that makes something the truth....it is what God says.
Firstly scripture does not state the old law has been abolished as plainly as Christians claim, but secondly and more importantly if you aren't Christian, then you don't consider the New Testament scripture on the same level.
Of his Jewish countrymen Paul wrote...
"Brothers, the goodwill of my heart and my supplication to God for them are indeed for their salvation. For I bear them witness that they have a zeal for God, but not according to accurate knowledge. For because of not knowing the righteousness of God but seeking to establish their own, they did not subject themselves to the righteousness of God. For Christ is the end of the Law, so that everyone exercising faith may have righteousness." (Romans 10:1-4)
Having a zeal for God, if it is misguided, is futile, no matter whether we profess Christianity, Judaism or Islam.
Judaism doesn't follow the New Testament because they don't believe Jesus was the messiah.
And The scriptures predicted this very thing. Only a remnant (Rom 9:27) responded to the Christian message and became the foundation of a "royal priesthood and a holy nation". Jews are still waiting for Messiah's first appearance, whereas Christians are waiting for his second and final coming to judge the world. Even then, not all are acceptable (Matt 7:21-23)
Not believing in him, does not make him go away, nor does ignorance cancel out the permanence of the judgment. (2 Thess 1:6-9)
Muslims have scripture called the Koran, but quoting the Koran to a non Muslim is as pointless as quoting the New Testament to a non Christian.
The Islamic faith is somewhere in the middle, but like Judaism, zeal for God, if it is based upon a wrong premise, gained from the wrong teachers, will not save anyone.
All these religions pray to God (whomever they perceive him to be) with hands dripping in blood. Jesus taught peace and love. (John 13:34, 35)
I'm neither Christian, Judiast or Muslim, but I respect the differences. There is no right or wrong here because all three consider "scripture" to be different things which is why I concentrate on the history of the text and not simply what the text says. Quoting scripture doesn't make it scripture if you aren't from a faith that considers it scripture.
That is entirely your choice. God provides his word to guide his people. "By their fruits" Jesus said we would identify God's true worshippers. They will be the ones living in peace with their neighbors, no matter whether their government identifies someone of another nation as an enemy or not. We will seek peace as far as it depends upon us. (Rom 12:17-21) We refuse to participate in war. (Isa 2:2-4)
Yet even in the New Testament there is no command to honor the memorial of Christ's death. There is history of what we call the Last Supper, but no command to follow it an an annual basis.
Paul wrote...
"For I received from the Lord what I also handed on to you, that the Lord Jesus on the night on which he was going to be betrayed took a loaf, and after giving thanks, he broke it and said: This means my body, which is in your behalf. Keep doing this in remembrance of me. He did the same with the cup also, after they had the evening meal, saying: This cup means the new covenant by virtue of my blood. Keep doing this, whenever you drink it, in remembrance of me. For whenever you eat this loaf and drink this cup, you keep proclaiming the death of the Lord, until he comes. (1 Corinthians 11:23-26)
Since this inauguration of the new covenant replaced the old covenant with its Passover celebration, Jesus as the true Passover Lamb, was asking that his death be commemorated in the same manner....yearly.