Paul's understanding of the creation scriptures cause him to declare that;
#1 sin was in the world before the law. It was not accounted as breaking of law, because there was no law. Rom 5:13(For until the law sin was in the world: but sin is not imputed when there is no law. My additional comments to that text are; "Sin was labelled as "sin"according to the words used in scripture when Cain thought to kill Abel.
Sin was labelled as "wickedness, "evil," "vain imagination" according to the words used in scripture that explains why God to send the flood to wipe out humanity on earth.
There is no hint that man broke God's law and sabbath, or your commentary would be correct." If there was a law declared we'd all be aware of what God commanded in creation.
The text proves that free will and dominion given to man, was corrupted by Adam's sin, and man mostly chose evil over good. Moses wrote as follows;
Gen 6:5¶And GOD saw that the wickedness of man [was] great in the earth, and [that] every imagination of the thoughts of his heart [was] only evil continually.
Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Gen 6:7 And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them. )
Did God say....They wont keep my commandments? NO!!!!

Paul further explains what Genesis through Exodus also proves...
Rom 5:14Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come.
So we can understand that God did judged sin, from Adam to Moses and the penalty of sin was death.
I expect you and others to apply your commentary to the word "trangression" as if a law was given, but the scripture is explaining the opposite.

The question is asked:
Gal 3:19 Why serveth the law?
Paul explains elsewhere that the law came 430yrs after the promises to Abraham because of transgression of the Children of Israel.
Paul explains here that the law served
until the seed came.