Contemporary English Version (CEV)
So for the sake of statistics: At this point, there have been four people on earth. One of them has been brutally killed by his brother. That's a 25% homicide rate. Not the best start for humanity. Can you picture God shaking his head, wondering what he has let loose upon the earth?
I've always wondered why Cain's offering does not please the Lord, and one way to look at it is that Cain brings his offering with an ungrateful attitude. Cain makes his offering begrudgingly, thinking that God will be satisfied with his actions and the condition of his heart doesn't matter. Cain gives, but resents having to do so.
I've done this before -- I've showed up at church frustrated, wishing I was off doing something else, but still with the mindset that God should bless me because I'm there. I'm following the letter of the law, but not the spirit of it.
God wants to capture our hearts and imaginations. God desires a loving relationship, founded on us being intrigued by God and pursuing him with love. Our offerings should flow forth from gratitude, and our songs should rise from love. Going through the motions doesn't bring praise to God -- God doesn't need our offerings. Our hearts and lives, offered freely to God, are what bring glory to God.