Charles Spurgeon Commentary 1 John 3:12

"not as Cain was of the evil one, and slew his brother. And wherefore slew he him? Because his works were evil, and his brother`s righteous." — 1 John 3:12 (ASV)

Not as Cain, who was of that wicked one, and slew his brother.

And wherefore slew he him? Because his own works were evil, and his brother's righteous.

That was the real evil at the bottom of his great crime; it was the wickedness of Cain's character that made him hate the good that was in Abel; and, therefore, after a while, he slew his brother, because his own works were evil, and his brother's righteous.