John Calvin Commentary Genesis 4:8

"And Cain told Abel his brother. And it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him." — Genesis 4:8 (ASV)

And Cain talked with Abel his brother. Some understand this conversation to have been general, as if Cain, treacherously concealing his anger, spoke in a brotherly manner. Jerome relates the language used: ‘Come, let us go outside.’ In my opinion, the speech is elliptical, and something is implied, yet what it is remains uncertain.

Nevertheless, I am not dissatisfied with the explanation that Moses concisely rebukes the wicked treachery of the hypocrite, who, by speaking familiarly, presented the appearance of brotherly harmony until the opportunity to commit the horrid murder arose.

And by this example, we are taught that hypocrites are never more to be feared than when they condescend to converse under the pretense of friendship; because when they are not permitted to harm by open violence as much as they wish, they suddenly assume a false appearance of peace. But it is by no means to be expected that those who are like savage beasts towards God should sincerely cultivate true friendship with men.

However, let the reader consider whether Moses did not instead mean that although Cain was rebuked by God, he nevertheless argued with his brother, and thus this statement of his would depend on what had preceded. I certainly lean more towards the opinion that he did not keep his malicious feelings within his own heart, but that he burst out in accusation against his brother and angrily declared to him the cause of his dejection.

When they were in the field. From this we gather that although Cain had complained of his brother at home, he had nevertheless so concealed the demonic fury that burned within him that Abel suspected nothing worse, for Cain postponed vengeance to a suitable time. Moreover, this single guilty act clearly shows where Satan will rush men when they harden their minds in wickedness, so that in the end, their stubbornness deserves the most extreme punishment.