How do you explain the universal language used by Paul in Romans 3:19-20 and the singular "Law"?
19 ¶ Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.
20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
There's nothing to explain.
Every man is under law.
Even those without Torah are a law unto themselves.
But the Torah was given to the Jews, not gentiles.
The Universal Moral Law is eternal, universal, understood by all man and not disputed.
Moses didn't give "mankind" that law, he gave God's covenant people their Torah.
Do you labour under the assumption that "Thou shalt not murder" was some unique new revelation not ever comprehended by man?
Did Moses have to flee Egypt after killing the Egyptian because Pharaoh read the Pentateuch?
Did Cain fear losing his life because of what was written in Exodus 20?
Does Genesis 9 prescribe the death penalty for the shedder of blood because of the Ten Commandments?
God doesn't need the Torah to condemn, it wasn't written to you anyway.