Genesis 4 - 10

After Adam and Eve were drove out of the Garden of Eden, the Lord -

"...gave unto them commandments, that they should worship the Lord their God, and should offer the firstlings of their flocks, for an offering unto the Lord. And Adam was obedient unto the commandments of the Lord." (Pearl of Great Price Moses 5:5)

So from the very beginning, a commandment or a law of sacrifice was given to Adam -

"...And after many days an angel of the Lord appeared unto Adam, saying: Why dost thou offer sacrifices unto the Lord? And Adam said unto him: I know not, save the Lord commanded me." (Pearl of Great Price Moses 5:6)

And Adam was given this explanation -

"...This thing is a similitude of the sacrifice of the Only Begotten of the Father, which is full of grace and truth.
8 Wherefore, thou shalt do all that thou doest in the name of the Son, and thou shalt repent and call upon God in the name of the Son forevermore..." (Pearl of Great Price Moses 5:7 - 8)

It becomes apparent that this law or offering was very specific in its compliance for -

"...Cain brought of the fruit of the ground an offering unto the LORD.
4 And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering:
5 But unto Cain and to his offering he had not respect." (Old Testament Genesis 4:3 - 5)

The commandment given to "offer the firstlings of their flocks, for an offering unto the Lord" was very clear. Anything else would fall under disobedience. Since the Lord gave no respect to Cain's offering because of his flagrant disobedience -

"...Cain was very wroth, and his countenance fell..." (Old Testament Genesis 4:5)

And in response, the Lord very objectively states the plan of happiness or unhappiness -

"...If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door..." (Old Testament Genesis 4:7)

It all hinges on obedience -

"...Wherefore, men are free according to the flesh; and all things are given them which are expedient unto man. And they are free to choose liberty and eternal life, through the great Mediator of all men, or to choose captivity and death, according to the captivity and power of the devil; for he seeketh that all men might be miserable like unto himself." (Book of Mormon 2 Nephi 2:27)

We learn that -

"...Noah was a just man and perfect in his generations, and Noah walked with God." (Old Testament Genesis 6:9)

All because of his obedience for -

Thus did Noah; according to all that God commanded him, so did he.
(Old Testament Genesis 6:22)

As a result the Lord promised -

"...will I establish my covenant; and thou shalt come into the ark, thou, and thy sons, and thy wife, and thy sons' wives with thee.
19 And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female.
20 Of fowls after their kind, and of cattle after their kind, of every creeping thing of the earth after his kind, two of every sort shall come unto thee, to keep them alive." (Old Testament Genesis 6:18 - 20)

And even as Noah and his family was preserved and left the Ark, in a great example of continued obedience -

"...Noah builded an altar unto the LORD; and took of every clean beast, and of every clean fowl, and offered burnt offerings on the altar." (Old Testament Genesis 8:20)