Jesus told his disciples "privately" (Matt. 24:3) to pray that the end times would not require a Sabbath flight (Matt. 24:20), knowing that they would be Christians at that time.
Since Jesus was addressing Jews who were still bound to the law and the old covenant, Sabbath rules would apply until the law was done way with by Jesus’ sacrificial death. When giving his instructions, his Jewish disciples would likely have wondered about traveling on the Sabbath. Prayer would put their mind at ease. But when instituting the new covenant, Jeremiah foretold that it was
not going to be like the old one. (Jer 31:31-32)
Since this was prophesied, why assume that anything under the old covenant was going to be binding on those who came under the new one?
“Christ is the end of the law” because he fulfilled it. All of the main principles of the laws were contained in Jesus’ teachings and covered under ‘the law of love’……love for God and neighbor…..no longer a written law but now engraved on hearts and governed by conscience.
For Jews, who had spent their whole lives observing the Sabbath, there was no mandate to cease doing so. But for Gentiles, there was no mandate to observe a Sabbath.
So, retaining the Sabbath law that only applied to Jews, was not incumbent on Gentiles. The majority of Christians in the first century were Jews, but once the Gentiles were brought into the Christian arrangement, there was no reason to keep a law that God applied only to his covenanted people and observed only after their release from slavery in Egypt, when they entered into the old covenant through its mediator, Moses.
It's clear that Christians being required to keep the Sabbath doesn't fit your philosophy, so you are going to ignore the logical meaning of Matt. 24:20 no matter what.
Logically, if there was a mandate for Christians to keep the Sabbath, the apostles, who were the first to be included in the new covenant, would have conveyed it in their teachings, which were for Jews as well as Gentiles.
When a group of former Pharisees who had converted to Christianity wanted to mandate circumcision and observance of the law of Moses (which included the Sabbath) to Gentile converts to Christianity, (as that was the law for Jewish converts) it caused quite a lot of controversy.…..but when the apostles and elders met in Jerusalem to sort out the dilemma…..
Read Acts 15:1-33….
”So the apostles and the elders gathered together to look into this matter. 7 After much intense discussion had taken place, Peter rose and said to them: “Men, brothers, you well know that from early days God made the choice among you that through my mouth people of the nations should hear the word of the good news and believe. 8 And God, who knows the heart, bore witness by giving them the holy spirit, just as he did to us also. 9 And he made no distinction at all between us and them, but purified their hearts by faith. 10 So why are you now making a test of God by imposing on the neck of the disciples a yoke that neither our forefathers nor we were capable of bearing? 11 On the contrary, we have faith that we are saved through the undeserved kindness of the Lord Jesus in the same way that they are.” . . . .
13 After they finished speaking, James replied: “Men, brothers, hear me. 14 Symʹe·on has related thoroughly how God for the first time turned his attention to the nations to take out of them a people for his name. 15 And with this the words of the Prophets agree, just as it is written: 16 ‘After these things I will return and raise up again the tent of David that is fallen down; I will rebuild its ruins and restore it, 17 so that the men who remain may earnestly seek Jehovah, together with people of all the nations, people who are called by my name, says Jehovah, who is doing these things, 18 known from of old.’ 19 Therefore, my decision is not to trouble those from the nations who are turning to God, 20 but to write them to abstain from things polluted by idols, from sexual immorality, from what is strangled, and from blood.”
All of the recommendations given at that meeting pertained to Gentiles, because the Jews already observed those things under their law. No Sabbath observance was part of the “necessary things” outlined by the apostles (Vs 28-29)……if it was “necessary”, they would have said so.
If SDA’s wish to observe a Sabbath, then no one is going to say that they cannot, because there is no law against it…..but if SDA’s want to mandate it for others, then that is a problem because they are then doing what those Jewish Christians did to their gentile brothers in the first century, trying to force on them the observance of a law that was not given to them and which the Jews themselves were not capable of observing perfectly anyway. The account in Acts is I believe, the principle upon which all of this hinges.
Jesus is “Lord of the Sabbath”, because it is his rulership in the administration of God’s Kingdom government, that will bring the 7th day of God’s rest to a successful completion. There are no specific “holy days” for Christians, who can serve God every day, by the way they live their lives 24/7.