ASV notes on Genesis 4:4-6
God always looks to the heart to know that the action is genuine, in this case, that Abel meant to please God with the best he had. You cannot fool God with long prayer or that many are praying at the same time, or good behaviour, nice clothing and persuading speaking. How usual is it today that uneducated fishermen are leaders in churches. What matters to men does not necessarily mean that God approves it. But don’t misunderstand me, Paul, the apostle was highly educated and wrote half the New Testament.
What’s important are not what we do, but the will and thoughts behind it? If what’s in our mind is in our heart it leads to action without expecting to be applauded by men and the society, and then what you do pleases you, you feel good and God blesses you if Jesus is in you. But you may say, Jesus was not in Abel. This is the same question as asking how Abraham was saved without Jesus saving him from his sins. It is like buying, using a credit card, you have no money, but you have credit and can purchase things. God did credit Abel and Abraham for what Jesus was going to do about 2000 or 4000 years later. God does not threat people differently; He is a fair and good God.
Cain offered his offer to God and when God corrected him he did not change his attitude, he did not acknowledge God as God who knew everything what was best for Cain. Cain thought God treated him unfairly; he valued his own opinion more than God’s and this mismatch between his thinking and What God expressed to him made him mad.
This anger came from inside and when anger and hostility comes from inside, from the heart it affects your appearance, people can observe it, it is visible, like God noticed it; “he looked annoyed and hostile”. Our problem is that we do not notice how we look, but our appearance is leaking our inner secrets. It is best for you to change your inside to improve your outside to correspond with the personality of Christ.
God said to Cain that he had no reason to be angry, it is simple, just believe in Me as God, receive what I am telling you and everything will be a blessing to you. But the sin was in the air.