Just a simple reading of the Council of Nicaea shows they decided then and there to ditch Biblical days and observe pagan days. Here is a direct quote:
We also send you the good news of the settlement concerning the holy pasch, namely that in answer to your prayers this question also has been resolved. All the brethren in the East who have hitherto followed the Jewish practice will henceforth observe the custom of the Romans and of yourselves and of all of us who from ancient times have kept Easter together with you.
In actuality, they forbid Bible believers from worshiping God's Feast days called for in Leviticus 23 and substituting their own made up days. They were antisemitic. Socrates wrote that up until this time the Christian church observed the 7th Day Sabbath everywhere except Rome and Alexandria. The take over of the Christian church by Constantine in Rome forced Christians to ditch the teaching of the Bible for made up dogma from Rome or suffer death.
Worship of Babylonian gods was not new in Scriptures. Read Ezekiel 8 and see the abominations in the Temple. God was unhappy with the Tammuz worshipers and then God describes a Sunrise service as an an abomination.
As Paul was the Apostle to the Gentiles, his quest was to get ex pagans to follow the Bible. They hung on to their old superstitions and drug them into the church. As a Bible believing Christian you should understand where myths and superstitions come from and follow the teachings of God in the Bible.
Just as an example.....
Jer 10:2 Thus says the Lord: "Do not learn the way of the Gentiles; Do not be dismayed at the signs of heaven, For the Gentiles are dismayed at them.
Jer 10:3 For the customs of the peoples are futile; For one cuts a tree from the forest, The work of the hands of the workman, with the ax.
Jer 10:4 They decorate it with silver and gold; They fasten it with nails and hammers So that it will not topple.
Jer 10:5 They are upright, like a palm tree, And they cannot speak; They must be carried, Because they cannot go by themselves. Do not be afraid of them, For they cannot do evil, Nor can they do any good."
When you study the Bible very long, you start to see that pagans worshiped under trees and worshiped trees. Jewish kings were admonished to destroy these worship trees "in high places" and in valleys. A "high place" was a place of worship for a pagan and they would have "Totem" like poles carved to worship.
I frankly don't know what a "SDA scholar" is, but you can probably find anyone to say anything anywhere. I go by the Bible as what to rely on. It's always fascinating to me to find people that read a verse they don't like and start quoting some "scholar" from the 12th century. All I know is God told us 100 times that the 7th day Sabbath was His blessed day and thought it important enough to put it as the 4th Commandment in the Decalogue. Since Jesus is the only Mediator between God and man, no man can change Scripture. I'll continue to rely on Scripture. There is no "Christmas" and no "Easter", but if you chose to observe the birthday of Jesus why not observe it on the day He came to live with us in human form?( Jesus has no beginning and no end) He was named Immanuel because He came to Tabernacle with His people. Tabernacles will always refer to the time God lives with His people. If you wish to observe His death, observe Passover. His resurrection? First Fruits. God has provided the days in Leviticus 23 that he will perform Biblical events. Random made up days have no Biblical meaning. Rapture will happen on some Feast of Trumpets in the future. Many Christians say it could happen any day, but we need to be watching for this day. We watch for His coming in Elul when the King is in the field, and be ready for Trumpets to go with him. Trumpets is the Day Jews know as no one Knows the Day or the hour, just as an American knows "Turkey Day" is Thanksgiving.
The reason the Sabbath is so important is to tell God's people that Jesus will return to rule and reign for 1000 years on or around 5999-6000 on the Biblical calendar. The Antichrist will change the Laws and calendar to confuse the church.(Daniel 7:25) Don't follow a man's teaching to avoid catastrophe.
Joh 5:43 I have come in My Father's name, and you do not receive Me; if another comes in his own name, him you will receive.
Stay with Scripture as Jesus is the Word and is telling you the Truth. "If you love Me, do my Commandments." Did Jesus tell you to worship on the Sabbath or the first day of the week? There is no Christmas or Easter in Scripture. They are made up men's days.
"New moons and sabbaths" are referring to Jewish feasts. I'm surprised you don't know that.
Easter and Passover NEVER are observed n the same day.
Actually, that isn't quite true. Passover is the 14th of Nisan. Nisan, like all Jewish months, begins with a new moon (see above), so, since the lunar cycle is 28 days, Passover is going to be close to a full moon.
Easter is the first Sunday after the first full moon after the vernal equinox (which Nicaea artificially fixed on March 21; it's really a day or two before that). So Easter is also going to be a week or less after the full moon. It isn't always the same full moon as Passover, but it often is.
For example, this coming year, Passover starts on April 15, which is Good Friday, and ends on Saturday, April 23. (Easter is obviously April 17.) You really can't get any closer than that. (Note that the Scripture is very clear that the resurrection happened on a Sunday morning).
The Orthodox rules for determining the date of Easter, I believe, prohibit it from coinciding with Passover. The Western rules do not.
There are 613 Mitzvot in the Torah. Why do you think those ten Mitzvot (actually more like 14) are special? Who told you that the commandment to keep holy the Sabbath day was more important than the commandment not to mix wool and linen?
Answer: the Christian Church did, and really, this was long before the Reformation, so let's just be honest and say it was the Catholic Church that did it. Why? Because those commandments clearly codify the basic natural moral law that all humans are expected to follow. Murder didn't become wrong because God said so in the Ten Commandments, it was wrong all along (Cain, call your office ...). Same for adultery and stealing.
However, there's an exception. (Actually, there's two, but let's keep it simple.) Nothing in natural law tells you that Saturday is the day to keep holy, and not Thursday or maybe the second and fourth Tuesday of every month, or whatever. That is why the church determined very early on that, while natural law can argue that time ought to be sanctified by, e.g., setting aside a day every week for the worship of God, the specific setting aside of Saturday was ceremonial law given to the Jewish people only, not to everyone.
Which is why Christians have gathered for worship on Sundays since before the last apostle was cold and stiff. It's just a fact. It's not "Babylonian" or any garbage like that. It's common Christian practice to meet on the first day of the week, the day when Our Lord was raised from the dead.