“He can’t help it. It’s not his fault,” Abel tells Goldie the gargoyle. “It’s who he is. It’s who we are. The first murderer and the first victim. This is our story.”
While Cain is harsh, bitter, and perhaps angry at the world, Abel is forgiving, sweet, warm-hearted, and a bit timid.
“I don’t mind getting murdered, honestly,” he says. “If that’s what makes Cain happy, then — hey, what are brothers for?”
Source: https://www.distractify.com/p/why-does-cain-keep-killing-abel-the-sandman