The Sabbath was a shadow that pointed forward to the 'rest' only found in Christ.
Paul's understanding of 'law' was the entire law or the Torah not the ten commandments only as SDA and others teach.
Tell me, ye that desire to be under the law, do ye not hear the law? For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman. Gal. 4:21,22
Paul understood law to be the first five books of Moses because the story of Abraham and his two sons comes from Genesis and the law was not given to Israel until Exodus. Believers are not under any aspect of the OT law.
I presume that Paul was not a hypocrite. If he preached that "Believers are not under any aspect of the OT law" then he would have lived what he preached.
If the Sabbath was nullified by Paul himself then surely Paul would have preached the gospel any day of the week, with no preference for the sabbath such as described here...
Act 17:2
And Paul,
as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures.
And Paul was just keeping the Sabbath with Sabbath keepers here, because he wanted to teach them they were no longer under the law....
Act 13:13
Now when Paul and his company loosed from Paphos, they came to Perga in Pamphylia: and John departing from them returned to Jerusalem.
Act 13:14
But when they departed from Perga, they came to Antioch in Pisidia, and
went into the synagogue on the sabbath day, and sat down.
And after instructing the Jews that they are no longer under the law, the Gentiles want to hear more, so Paul has the perfect opportunity to say, "Well see you tomorrow, Sunday, since all days of the week are now alike". That should be the case, but what do we see?
Act 13:42
And when the Jews were gone out of the synagogue, the Gentiles besought that these words might be preached to them
the next sabbath.
Act 13:43
Now when the congregation was broken up, many of the Jews and religious proselytes followed Paul and Barnabas: who, speaking to them, persuaded them to continue in the grace of God.
Act 13:44
And
the next sabbath day came almost the whole city together to hear the word of God.
Is this a one-off or does Paul have a pattern of hypocrisy, preaching against the law, and the Sabbath, yet secretly keeping it?
Act 16:13
And
on the sabbath we went out of the city by a river side, where prayer was wont to be made; and we sat down, and spake unto the women which resorted thither.
Act 16:14
And a certain woman named Lydia, a seller of purple, of the city of Thyatira, which worshipped God, heard us:
Paul, the great law-looser sure has a strange way of behaving for one who says we are no longer bound to the Sabbath.
Act 18:4
And he reasoned in the synagogue
every sabbath, and persuaded the Jews
and the Greeks.
Even the Greeks are forced to keep the Sabbath to hear Paul.
And if Paul preached against law keeping, the annual, Jewish Sabbaths would have been out of the question for Paul, since these were even iffier twigs of the law.
Act 18:21
But bade them farewell, saying,
I must by all means keep this feast that cometh in Jerusalem: but I will return again unto you, if God will. And he sailed from Ephesus.
Could Paul possibly still, as a hypocrite be keeping the Jewish Feast of Pentecost?
Act 20:16
For Paul had determined to sail by Ephesus, because he would not spend the time in Asia: for he hasted,
if it were possible for him, to be at Jerusalem the day of Pentecost.
Not only does Paul want to keep these feast days, he wants to keep them in Jerusalem, where they were commanded to be kept.
And when Paul gets to Jerusalem, he finds that he has a reputation for doing away with the law.
Act 21:21
And they are informed of thee, that thou teachest all the Jews which are among the Gentiles to forsake Moses, saying that they ought not to circumcise their children, neither to walk after the customs.
Here is the perfect opportunity for Paul to say that he, as a born again believer is no longer under the OC law.
But what does Paul do? He goes to the temple and joins with Jews implementing an OC vow.
Act 21:22
What is it therefore? the multitude must needs come together: for they will hear that thou art come.
Act 21:23
Do therefore this that we say to thee: We have four men which have a vow on them;
Act 21:24
Them take, and purify thyself with them, and be at charges with them, that they may shave their heads:
and all may know that those things, whereof they were informed concerning thee, are nothing; but that thou thyself also walkest orderly, and keepest the law.
Woah!! Hold your whole team of horses. Did I read that right that the great preacher against the law "walketh orderly, and keepest the law"?
So Paul goes through some OC ritual with these law keepers, to make a point that he DOES, HIMSELF keep the law.
But all is not lost, because read the next verse where it seems that Paul keeps the law, but Gentiles don't have to.
Act 21:25
As touching the Gentiles which believe, we have written and concluded that they observe no such thing, save only that they keep themselves from things offered to idols, and from blood, and from strangled, and from fornication.
Well there we have it. Gentiles only have the OT-lite version of the law.
So everything that Paul wrote against the law was pure hypocrisy, because Paul kept the law himself, to the letter, yet told Gentiles they don't need to.
In case you missed it, I was being a little facetious.