In reading Proverbs 15, verse 8 stood out:
"The sacrifice of the wicked is an abomination to the LORD: but the prayer of the upright is his delight."
This reminds me of Cain, and how he brought his "sacrifices" to God, and yet was insulting God in the very act of it because he was blatantly disobeying and disregarding God. He was, in essence saying, No God, i'm going to do this MY way. Who are YOU to tell me what to bring to You or HOW, or in what kind of attitude. You should be glad i brought you ANYTHING.
Now Cain KNEW what God required. YET he stubbornly refused.
And the bottom line is, that he had no regard for God, or fear (respect) for God, or love in his heart for God, but he despised God.
He didn't even seek repentance.
Not once.
Even after he killed his brother, he didn't repent.
This is what i thought of when i read the first part of verse 8:
"The sacrifice of the wicked is an abomination to the LORD"