It's a lot to answer and having worked for 30 years at a job that placed inordinate demands upon my mental faculties, I now suffer from frequent bouts of very low attention span, but I'll do the best I can for a someone who has been so friendly toward me.
It seems that our histories are very similar, but in reverse. Coming from a family of Southern Baptists (in eastern Tennessee), I believed somewhat as you do now, I guess. We considered ourselves New Testament Christians. The first Bible I owned was a copy of the New Testament with Psalms and Proverbs included. Respectable behavior was the standard and was expected, and the Sabbath commandment was applied to Sunday. Until I was 26 years old, I thought Sunday was the Sabbath. There was no Internet to tell me otherwise. All I knew was that people rested on Sunday and went back to work on Monday.
I haven't studied much of Paul's writings very deeply. Frankly, I find it frustrating because of how much arguing goes on about them. And I think I know why but when I bring it up I always get shut down hard. I really wish Peter had talked more about why when he mentioned that Paul writes many things that are hard to understand. He does give a clue, though, in the context:
2 Peter
14So then, dear friends, since you are looking forward to this, make every effort to be found spotless, blameless and at peace with him. 15Bear in mind that our Lord’s patience means salvation, just as our dear brother Paul also wrote you with the wisdom that God gave him. 16He writes the same way in all his letters, speaking in them of these matters. His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other Scriptures, to their own destruction. 17Therefore, dear friends, since you have been forewarned, be on your guard so that you may not be carried away by the error of the lawless and fall from your secure position. 18But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be glory both now and forever! Amen.
As far as the two passages of Scripture you quoted, I have to be honest: I studied these two along with nearly every other objection that has ever been given to commandment-keeping before I became an Adventist. I was young and had a mind like a spongue and I was fortunate enough to have access to a church which had a library filled with old books by Adventist pioneers on these very subjects. They were so ripe with truth I could barely believe what I was reading. They were written at a time when Christians had much less to occupy their minds than the massive media glut we have now. There was much, much more Scripture quoted compared to the over-analysis and opinions we find in new books about Biblical studies. There were non-Adventist books, too, which didn't seem much different to me, except that the word "Sunday" sometimes replaced "Sabbath." Being uninitiated in who were Adventist and non-Adventist authors, oftentimes I would read half-way through a book before I would realize it was non-Adventist.
I found out from a combination of reading these books and studying my Bible that the difference between positions on the status of the law in Christianity was based on mainly 2 factors: an argument over whether the language in any given text was figurative or literal; or that when these texts were written by Paul, especially, were they using the "all things to all men" hyperbole, figure-of-speech method Paul spoke of in 1 Corinthians 9:22?
Much of the confusion in Christendom takes place because of the Luke 10:21 "wisdom hidden from the wise" concept that my friend @bbyrd009 so loves to cite. It is caused by folks in high religious places who are not converted, but simply wish to appear wise about Bible religion, IOW, a method of hating God that passes for a method of loving Him. The obvious problem with this is the fact that it causes a trickle-down effect upon innocents who are simply doing the best they can for reading material apart from the Bible Itself. And we all read other books.
But back to the 2 passages.
I believe a good way to understand 2 Corinthians 3 is in light of a similar passage:
Romans 7
7What shall we say, then? Is the law sinful? Certainly not! Nevertheless, I would not have known what sin was had it not been for the law. For I would not have known what coveting really was if the law had not said, “You shall not covet.” 8But sin, seizing the opportunity afforded by the commandment, produced in me every kind of coveting. For apart from the law, sin was dead. 9Once I was alive apart from the law; but when the commandment came, sin sprang to life and I died. 10I found that the very commandment that was intended to bring life actually brought death. 11For sin, seizing the opportunity afforded by the commandment, deceived me, and through the commandment put me to death. 12So then, the law is holy, and the commandment is holy, righteous and good.
Is Paul talking about actually giving up the ghost here? No, he is talking about conviction, which is the same thing being spoken of in 2 Corinthians 3.
What about the glory of Moses's countenance? Is it the same as the glory of what is being reflected, the law? No, Paul just said the commandment is holy, righteous, and good. The glory of Moses's face faded away because he was mortal. So the ministry of death referred to in 2 Corinthians 3 must be something else. Could it be the ministry of conviction, alluded to in Romans 7? Well it would make more sense, since the law itself doesn't kill but teach that sin is present which, in turn, causes death.
Also, if 2 Cor 3 meant that the law is fading away, wouldn't all ten of the commandments become null and void? I don't see anything in the text that suggests it is restricted to the 4th article of the law.
As far as Galatians 4:22-31 is concerned:
Agreed
No, the law of God and the law of sin and death are not the same.
This is the law of sin and death:
The one who sins is the one who will die. (Ezekiel 18:20)
Again, conviction of cause and effect do not equal the ten commandments in content.
I don't know how deeply you studied Adventism, but what I get from it and what could be considered my basic philosophy is simply this: The conditions of eternal life are the same today as they always were and ever will be: Perfect obedience to the commandments of God. If it were not so we would need no savior. I don't particularly like boiled-down versions of philosophy (especially Christian) but it's the best I've been able to do.
