"Are you saying that what was mandated by God was in fact an instrument of deception by the devil?"
No, what was mandated by God was not an instrument of deception by the devil. It was exactly what Paul said, a tutor to lead the Jew to Jesus, who was the only One who could do the Law and was the only One who could justify. Rom.3:28,"For we maintain that a man is justified by faith apart from works of the Law." Even the men of old were justified by trust that God would solve their problem...not the Law.
And, yes, the Law is gone. Rom.7:6, "But now we have been released from the Law, having died to that by which we were bound, so that we serve in newness of the Spirit and not in oldness of the letter."
Serious misunderstandings of theology did, however, occur and are occurring in the world, all of which is guided by God. And, yes, of course, God is using Satan in those misunderstandings. Recall the "deluding influence" God will send. IIThess2:11 Further, you must admit one of us is seriously mistaken in this argument. Perhaps you believe truly sincere people will always find truth (your side), and thus you might question our sincerity. It does not feel to me as though either side is insincere. But, one of us, or perhaps both of us, are wrong. Is God doing the "deceiving" in one of us now? Well, evidently, yes. And, billions of other folks are wrong as well (Buddhists, Muslims, pagans, Zoroastrians, etc.).
This is, however, His perogative to guide His world the way He pre-planned to bring the most glory to Himself. It is not ego-maniacism, which is someone undeserving acting pompously. He really is the All in All. And, He is the Potter, we are the clay. Rom. 9. Some have been made for destruction, some for honor. Paul did not seem to think we deserved to have a gripe over this fact.
Thus, the Law of course could have been a means of holiness had any Jew been able to do it. Their broken natures (a picture of all humanity) mitigated against this possibility. None could, none would, none wanted to...at least that is what Paul noted their own Scriptures taught. Rom. 3.
Paul indeed stopped acting like a Jew. Rom. 10:4, "For Christ is the end of the Law for righteousness to everyone who believes." And, yes, he absolutely wrongly fell back into doing Law-bound actions (Acts 21). But, he said the Law was gone and was only suitable for teaching evil men how evil they were. ITim 1:9
Finally, I agree that Protestantism has reverted to some forms of the Law. They do, in fact, call certain buildings "sanctuaries", and they often create a "clergy". But, these are errors. And, to me Luther was nothing more than someone who noticed a part of the errors of his organization. He carried on with some of them; he corrected some of them. But, if these are reversions to the Law, Rome has clearly done this in spades.
Paul does not cease being a Jew, and we might even say that, since the Law—properly read— ends in obedience to Jesus, that Judaism is the only true religion. Our God is the God of Abraham , Issac and Jacob, not the god of the philosophers, of Plato and Aristotle, as Pascal remind us. Since the beginning, there have always been those who, like Marcion, wants us to cut out ties to the Jews. But here we are and here they are.