If the Weekly Sabbath was instituted at creation, doesn't that prove that it has been abolished?

Great Question.

Let me start by dealing with a few assumptions that are needed to understand the idea that Sabbath was instituted at creation.

The question has been written from the perspective that the writing by the finger of God is the authority, as opposed to the pen of Moses. This doesn’t represent authority, rather it represents priority. That is God wrote the things he knew were essential. In fact, if you read Exodus 20:1 you see that these are the only laws that God spoke out loud to the people. See v18-19 where they actually asked God not to do that again

However, the Authority comes from God, and God is immutable. (Malachi 3:6, James 1:17, Isiah 40:8). What this suggests is that the Law of God existed before the Sinai experience. So where did it begin? Well, based on the fact that God calls out creation in the fourth commandment(Ex 20:11) it seems logical to assume that the law of God existed at least at creation, and more than likely it is eternal and existed before creation.

Another assumption made is that the Ten Commandments in Deuteronomy are materially different to those in Exodus 20 and that they constitute a different type of law. The introduction to Deuteronomy written by the translators of the ESV states that Deuteronomy means “second law” and is a retelling and final address of Moses. That is they are essentially the same thing. Interestingly the Sabbath commandment is the only one that has any difference where in Deuteronomy it focuses on redemption, not creation.

In Exodus 34 we see new stone tablets that are taken up to Mt Sinai to be inscribed by God. This is also evidence that the commandments were written by God to be placed in the Ark of the covenant.

There was also a comment around parts of Leviticus 23:32. I assume that you are referring to the “from evening to evening” component of Sabbath. This is nearly the mechanics of Sabbath and as you mentioned is a reiteration of the mechanics of creation. Once again affirming the connection and pre-existence of the law of God before they were written down. Interestingly, this actually is a point of discussion around Adventists when you travel into the arctic circle in summer or travel East to Tonga over the dateline. https://www.ministrymagazine.org/archive/1966/01/why-seventh-day-adventists-keep-sunday-in-tonga

So after clearing that up (hopefully) you will better understand the Adventist perspective on the answer to your specific questions.

Do Seventh-Day Adventists believe the Old Testament law is divided into moral and ceremonial law?

This metaphor is used and is often misrepresented. There is a component of the law that tells us how to behave with God and with each other. The moral law. And a component that instructed the Israelites how to be the holy people of God. The ceremonial law. The 10 commandments are clearly moral law as it doesn’t contain any ceremonial practices. However, this is just a metaphor and there are other categories of ‘laws’ within the writings of Moses that are useful for health, relationships, and justice. These could be broadly categorised as community laws that ensure the community operates well.

Do they really believe that all of the ceremonial law is abolished?

The ceremonial law exists to point towards Christ. Hebrews 8:5 comments on this, that the earthly sanctuary was a pattern or metaphor for the heavenly. Since Jesus no longer needs a metaphor to describe his work, the ceremonial practices are no longer necessary.

However, the ceremonial law has principles that can be used to live a more holy life. For instance, Adventists recommend at least a clean food diet, but also take it a step further back to creation and recommend a vegetarian diet as well.

Do Seventh-Day Adventist have a list of which ceremonial laws are still in effect?

There are no ceremonial laws that Seventh-Day Adventist would say are in effect, rather principles to be observed, as you mentioned our food is one, where the principle of unclean meat still applies merely for the health benefit. While culturally most Adventists do not eat unclean meat, you would still be accepted into membership (in most places).

No adventist believes this:

Therefore, according to SDA definitions, the moral law of the ten commandments is only the second set of ten commandments, found in Deuteronomy 5:6-21. The first set of ten commandments from Exodus 20 were smashed upon the ground and never placed inside the ark. Therefore the commandments in Exodus 20 are ceremonial law, not moral law.

I'm afraid your inference is wrong. Exodus 20 is God's moral law. To get more detailed, the moral law is the ten commandments - the law of love expanded, the ceremonial laws were those made to point to Jesus and were fulfilled at the cross. Adventist like to highlight the difference by saying the ten commandments were written by God, and was at one point in the earthly ark of the covenant. But, they do not mean literally only the set in the ark of covenant is the moral law. Instead this is what they support: (the first part quotes John Wesley, founder of the Methodist church)

In answer to the claim that at the death of Christ the precepts of the Decalogue had been abolished with the ceremonial law, Wesley said: “The moral law, contained in the Ten Commandments and enforced by the prophets, He did not take away. It was not the design of His coming to revoke any part of this. This is a law which never can be broken, which ‘stands fast as the faithful witness in heaven.’ ... This was from the beginning of the world, being ‘written not on tables of stone,’ but on the hearts of all the children of men, when they came out of the hands of the Creator. And however the letters once wrote by the finger of God are now in a great measure defaced by sin, yet can they not wholly be blotted out, while we have any consciousness of good and evil. Every part of this law must remain in force upon all mankind, and in all ages; as not depending either on time or place, or any other circumstances liable to change, but on the nature of God, and the nature of man, and their unchangeable relation to each other. (The Great Controversy, Ellen White, pg 262)

The bold was added for emphasis. Therefore, the moral law always existed, and it is not the moral law spelled out on a dead stone that saves, but the moral law written in the heart. Paul declares:

not in tables of stone, but in fleshly tables of the heart (2 Cor 3:3)

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Adventist, like most Christians believe, we are under the new covenant of grace, the old covenant of obeying by our own powers is done away. However, the content of the moral law is still the same as always. By faith through grace God leads us to want to live according to the ten commandment. The fourth commandment (Exodus 20:8-11) specifically says to remember the Sabbath day because God blessed the Sabbath day at creation. It is different from the ceremonial laws pointing to Jesus, because the Seventh day Sabbath exists even if men never sinned, and was not fulfilled at the cross.

Exodus 20:11 For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it.

By the way, God's laws are not limited to just moral laws and ceremonial laws. There are also health laws for the body (still in effect today), and civil laws that applied only to the Israelite nation written in Moses book of laws.