ASV notes on Genesis 4:7-9
God said to Cain that if you do well, that is listen to Me it will go well for you, stay with Me, be close to Me, knowing Me, everything that is good for you is all about Me. But if not the sin will find you and stay at your door, like God puts it “sin crouches at your door; its desire is for you [to overpower you], but you must master it.” The devil is like a roaring lion, he is not a lion but roars like one, he is not dangerous if you know him, because Jesus triumphed over him on the cross.
But if anger and hostility hits us, the sin crouches at the door; this door that God’s talking about is the door to our heart. If we cannot resist the temptations provoked by our senses, it could be that we respond with anger and hostility to situations in our life, but it could also be trivial things in our daily striving, like overeating, too much alcohol, only thinking about ourselves and so on. The sin is always there, like God puts it, crouches at the door, and the sin is ready to take over your life and lead you away from God. God warned Cain and said that the sin will always be there ready to attack his week points, the sin are there but you must master it.
What is God talking about here; He is talking about disciplining ourselves from the temptations of the devil, which is what we cannot do in our own strength. Cain had God and could have turned to Him for help, but he didn’t. We cannot do it by ourselves either, but with Jesus in our heart we can rely on The Holy Spirit and ask for help and guiding, the quick method is praying in tongues, that is starting the turbo engine, and things will sort it selves out. See 1 Corinthians 14:4.
In Genesis 4:8 it looks like Cain is talking to Abel and asking him questions or to explain why God preferred Abel’s offer and not Cain’s, may be Abel said something like God loves me and I love Him and want Him to have the best I can give Him. May be Cain was thinking like “who do Abel think he is, better than me?” Christians may answer people in the same way, like God loves me and blesses me, God loves me like a loving Father, and sometime people get mad too like Cain and Christians are being killed.
When talking to Abel the anger hit Cain and he could not resist killing him thou it seems planned because he picked a time when they were alone, when Adam and Eve or God was not there, Cain went and talked with Abel.
In verse 9 we see that Cain is lying to God like not a big thing, the sin was being a part of him, he was a habitual sinner. We can also notice that talking to God was not unusual, it was common at that time, their spiritual awareness was lot stronger than we find today. Also it seems that Cain did not feel any gilt, like he had the right to kill Abel because he was being treated unfairly as he thought. We can just imagine and compare with the raising crime rate of today, seems like people think they are being treated unfairly all over the world. To see the result we can just watch the news. Innocent people are being killed more and more frequently. Abel was killed, and he also was innocent.