After the stories of creation and the banishment of Adam and Eve from the garden of Eden, the murder of Abel by Cain is described following their offering of sacrifices.
R’ SR Hirsch wrote that this was the first time that offerings were mentioned in the Torah. The offerings predated polytheism and were as old as mankind, a natural expression of human thoughts and emotions. Abel’s offering was accepted but Cain’s offering was rejected. The statement is “G-d turned to Abel and his offering but to Cain and his offering He did not turn”. Rashi wrote that the reason is in the text, stating that Cain brought an offering “from the fruit of the ground”, meaning that he did not make a special selection. In contrast, Abel “brought from the firstlings of his flock, and from the best of them”.
R’ Hirsch wrote that everything depends on the spirit with which the offerings or prayers are offered. Cain did not make a special selection whereas Abel selected from the very best. R’ Hirsch wrote that “he who offers the first and the best attaches primary importance to his relationship to G-d. Everything else in life is of secondary importance and offering the first is regarded as a substitute for dedicating all the rest”.
Nechama Leibowitz wrote that a man who has done wrong and senses his fault should be concerned to remedy it, especially when that is within his power. Instead Cain was angry and not with himself. G-d’s response to Cain’s “fallen countenance” was “surely if you improve yourself you will be forgiven, but if you don’t improve yourself, sin lies at the door. It’s desire is toward you , yet you can master it”. Nechama Leibowitz wrote that the message here was one of encouragement to mankind, stressing that mankind’s spiritual salvation lies within. There is always an opportunity to repent and mend one’s ways. Cain was not satisfied with the message contained in G-d’s words, and “rose up against his brother and killed him”.
Cain was banished, and condemned to a life of wandering. The clemency was attributed by Albo to the fact that he did not know the meaning of death or the consequences of his blows. Rashi commented that “the blood of your brother” indicated the elimination of Abel and his descendants. The Mishna, quoted by R’Munk pointed out the difference between civil law (where man makes restitution for a wrong he did and is pardoned) and criminal law(where the culprit is held responsible not just for the blood of the victim, but also of his descendants ever after) (Sanhedrin 4:5).