What does Genesis 4:4 mean?
Cain and Abel both have a relationship with the God who made their parents with His own hands. Both are bringing offerings to him. The previous verse tells us that Cain, the farmer, brought crops to the Lord: the fruit of the ground. Abel, the keeper of sheep, brought fat portions from a firstborn lamb from his flock.Details are scarce in this part of Scripture. Only the most basic information is being given. So, we don't know if God required some particular form of sacrifice, sacrifice at certain times, or of some quantity. As far as we know from this text, God may or may not have expressed His will about the kinds of offerings He would accept.
Later, under the Law of Moses, God will require Israel to bring very similar offerings as part of their worship of Him and to receive atonement for their sin. Those details are not mentioned in this passage, and we have no way of knowing if God gave such a requirement to Cain and Abel. That being said, it seems Abel's offering (Genesis 4:4; Exodus 13:12 more closely matches the requirements of this future law than Cain's (Genesis 4:3; Leviticus 2:12; Numbers 18:12). This may help to explain why the Lord approved of Abel's offering and looked on Abel with favor, above his older brother.