It’s almost certain that the giving of the Law at Mt. Sinai only formalized what had been understood since the beginning. Otherwise how would Cain and Abel have known to bring offerings to God, and what kind of offering was acceptable? (Genesis 4:3-7) And how would Noah have known clean animals from unclean ones? (Genesis 7:2-3) Or to offer a sacrifice as soon as he got off the Ark? (Genesis 8:20) Same with Abraham. The first mention of the virgin birth is in Genesis 3:15, and the first prophecy of the 2nd Coming was given by Enoch several hundred years before the flood (Jude 14-15).Also, the meanings of the names of the 10 Patriarchs in Genesis 5 make a sentence that tells the Gospel Story. “Man is appointed mortal sorrow, but the blessed God shall come down teaching that His death shall bring the despairing rest.”Then there’s the Mazzaroth, of which the study of astrology is a corruption (punishable by death in ancient Israel). In Hebrew, the 12 signs of the Zodiac tell the story of the Redeemer. Tradition has it that they were named by Adam, Seth, and Enoch to help fathers tell their sons of the coming Messiah while lying under the stars tending their flocks in pre-flood times.I could go on and on, but I think you get the point. Man has known from the very beginning what God expects of us and how He would restore us to His family. Just as it is today, it wasn’t from a lack of knowledge that people have perished, but from a refusal to believe and obey.